Selective and efficient bifunctional and trifunctional nanoporous catalysts

ABSTRACT

Selective and efficient multifunctional nanoporous catalysts containing spatially distributed organoamine and silanol groups, and methods of preparation thereof. The catalysts have been observed to be very highly efficient in catalysis of the Henry reaction.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority from U.S. provisional patentapplication Ser. No. 60/954,619 filed Aug. 8, 2007, the disclosure ofwhich is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Inventions described herein were developed under National ScienceFoundation Agreement No. CHE-0645348. The United States Government hascertain rights in these inventions.

This invention relates in one embodiment to postgrafting of spatiallyisolated catalytic groups on mesoporous materials to produce nanoporouscatalysts, and more particularly to selective and efficientmultifunctional nanoporous catalysts, and their methods of preparation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Selective and efficient multifunctional nanoporous catalysts and methodsof preparation thereof.

2. Description of Related Art

Multi-step and efficient synergistic catalytic processes to varioustypes of biomolecules by biological catalysts (enzymes) are very commonin living organisms. Many notable examples of such enzymatic andantibody catalytic processes involve acid-base cooperative or efficientbifunctional catalysts. By mimicking these extraordinary abilities ofnature, some conventional homogeneous bifunctional acid-base catalystshave been synthesized, such as those disclosed by Breslow et al. in J.Am. Chem. Soc. 1993, 115, 10988-10989. However, the efficiency andselectivity of these catalysts, which often depend on the relativeseparation distances between the acid and base catalytic sites, areoften poor because the materials lack a continuous range of acidic andbasic catalytic sites. Hence, a considerable amount of recent effort hasbeen directed towards the synthesis of heterogeneous solid-state,acid-base catalysts having well-controlled, high concentrations ofacidic and basic catalytic sites.

A family of mesoporous materials, which were first reported in 1992, hasbeen widely and effectively used as hosts for a variety of catalyticallyactive functional groups, including acidic and basic sites, to produceefficient heterogeneous catalysts. By postgrafting of the residualsurface silanol groups of the mesoporous materials with organosilanes,high surface area and tunable nanopores containing solid-acid andsolid-base mesoporous catalysts for reactions such as Knoevenagelcondensation, catalytic oxidation, and Michael addition have beensynthesized, as reported by Cauvel et al. in J. Org. Chem. 1997, 62,749-751; and Rao et al. in Angew. Chem. Int. Ed. 1997, 36, 2661-2663.However, to the best of the applicants' knowledge, almost allpostgrafting syntheses of catalysts reported to date are typically doneby stirring mesoporous materials with excess organosilanes in non-polarsolvents such as toluene or cyclohexane at reflux temperature, 112° C.

Postgrafting of organosilanes onto mesoporous materials in toluene inreflux indeed allows an effective inclusion of densely populated or highconcentrations of covalently bound organic functional groups, includingorganoamines. However, this synthetic approach also has drawbacks as itgrafts most of the surface silanol groups of the materials. The lattergroups, which can act as weak acids, generally increase the efficienciesof a number of organoamine catalyzed reactions such as the Henryreaction and nitroaldol condensations. Furthermore, the presence ofdensely populated organic groups reduces the surface areas and porevolumes of the materials. Therefore, densely populated organoaminecatalysts synthesized in toluene are typically accompanied by loss ofcatalytic efficiency. For instance, metallocene catalytic groupsimmobilized on densely populated postgrafted organoamine synthesized intoluene have lower catalytic efficiency for polymerization reactionsthan corresponding samples containing sparsely populated metallocenegroups, as reported by McKittrick et al. in J. Am. Chem. Soc. 2004, 126,3052-3053; and Hicks et al. in Chem. Mater. 2006, 18, 5022-5032.However, the synthesis of the latter materials involves a lengthymulti-step procedure consisting of preparation of bulky imine containingorganosilanes and postgrafting the groups in toluene to form denselypopulated imine functionalized mesoporous materials. Upon subsequenthydrolysis of the bulky imine groups, spatially ordered organoamines andsilanol groups are formed.

Recently, Katz et al. described the synthesis of organoaminefunctionalized silica gel catalysts containing silanol groups in J. Am.Chem. Soc. 2006, 128, 3737-3747. These bifunctional catalysts showedincreased efficiency and selectivity for the Michael and Henry reactionscompared to the corresponding materials without silanols. However, thesurface area of silica gel is low, the number of the bifunctional groupsin the material is limited, and the distribution of the two groups isdifficult to control. Davis et al. have also reported the synthesis ofsulphonic acid and organoamine bifunctionalized catalysts for nitroaldolreaction by self-assembly in Angew. Chem. Int. Ed. 2006, 45, 6332-6335.However, these materials have a low number of randomly distributed acidand base groups.

What is needed to address these problems is a catalyst material that canbe synthesized by a simple, straightforward process, that has bothacidic and basic functionality, and that has a high efficiency withrespect to catalyzed reaction rate and yield.

Additionally, many pharmaceutical and industrial catalytic processesinvolve multiple, similar reactants and competitive reactions while aproduct from one of the reactants or reactions is only needed. Theproduction of specific products by selectively catalyzing a specificreactant or reaction in a mixture of similarly reactive compounds orfrom competitive reactions is often necessary for the efficientproduction of various fine chemicals and industrial materials in highyields. Consequently, the development of selective catalysts and theefficient catalysis of one specific reactant have remained importantresearch areas in catalysis and materials science; however, achievingthese goals is often met with considerable challenges. For instance, byusing the differences in the sizes and shapes of the reactants and theirmass transport into the catalytic sites on solid zeolite poroussupports, many selective catalysts have been synthesized. However, dueto the narrow pore-sizes of zeolites, selective catalytic reactions ofonly smaller molecules are possible.

The recent advances in the synthesis of organic- andorganometallic-functionalized mesoporous metal oxides and imprintedpolymeric and imprinted metal oxide nanostructured materials have openedup synthetic strategies to novel selective catalysts. While thenanoporous structures in mesoporous materials enable size and shapeselectivity as in zeolites, the higher pore diameters and the largesurface areas in mesoporous materials further allow surfaceimmobilization of large numbers of various organic groups to tune thesurface properties and pore-diameters of the materials without severelyclogging the pores as in zeolites. Functionalization of these materialswith organic groups of specific hydrophobicity or hydrophilicitymodifies the immediate dielectric environment of the catalytic site andenables reactant of matching polarity to access the catalytic sites andundergo preferential catalytic reactions. For instance, byco-condensation of two organosilanes, Lin and co-workers report in J.Am. Chem. Soc. 1997, 119, 4090-4091 the synthesis of bifunctionalmesoporous organosilica materials that are selective to hydrophobicgroups. These materials, however, achieved the required selectivity witha maximum of 50% yields in over 24 h and selectivity only forhydrophobic reactants. Co-condensation procedures in synthesis ofmesoporous organosilica often results in poorly ordered mesostructures,which might be one of the reasons for the low yield of the Henry productby these materials. Very recently, Anwander and co-workers synthesizedfunctionalized mesoporous silicas with two steps grafting in non-polarsolvent, cyclohexane, to pore-size engineer cage like pores of SBA-15materials for size-selective catalytic transformations, as disclosed inChem. Eur. J. 2007, 13, 3169-3176. They used various sized long chainalkyl dimethylaminosilanes and organoaluminum compounds and theydemonstrate aluminum-catalyzed Meerwein-Ponndorf-Verley reduction ofdifferently sized aromatic aldehydes (benzaldehyde and 1-pyrenecarboxyaldehyde).

What is needed to address the problems where a single reaction pathwayand product is desired from multiple pathways and products is amultifunctional catalyst that has tunable selectivity and that is simpleand straightforward to synthesize.

SUMMARY OF THE INVENTION

The present invention meets certain previously stated needs by providingmultifunctional catalysts containing spatially distributed acid and basegroups grafted to a substrate. The substrate is preferably a mesoporoussubstrate with a high degree of porosity and a high surface area;however, other substrates such as silica microspheres or silica gels mayalso be used with similar outcomes of obtaining “spatially distributed”groups. The respective acid and base groups are preferably silanolgroups and organoamine groups. The substrate is preferably a form ofmesoporous silica. These catalysts have been observed to be very highlyefficient in catalysis of the Henry reaction. Additionally, certaincatalysts are provided which have tunable selectivity for hydrophilic orhydrophobic reactants. Additionally, certain catalysts are providedwhich have optimized cooperative acid-base bifunctionality.

In accordance with the present invention, there is further providedmethods of synthesizing such catalysts. In one embodiment, the synthesiswas achieved by carrying out either a simple, one-step postgrafting ofexcess aminoorganosilanes under reflux onto mesoporous silica in apolar-protic solvent, ethanol, at a lower temperature, 78° C., than istypically used in prior art synthetic methods. In another embodiment,the synthesis was achieved by postgrafting lesser amounts ofaminoorganosilanes in toluene in shorter reacting time than prior artsynthetic methods, at 78° C.

In other embodiments, the synthesis of catalysts of high efficiency maybe accomplished by postgrafting of organoamine groups on the mesoporoussubstrate at a density of between about 6 and about 15 percent of theavailable silicon sites. In another embodiment, the synthesis may beaccomplished by performing the organoamine postgrafting reaction in apolar-protic solvent. The solvent may be a low molecular weight alcohol,such as methanol, ethanol, and preferably isopropanol. In anotherembodiment, the synthesis may be accomplished by performing theorganoamine postgrafting reaction in a dipolar-aprotic solvent, mainlyacetonitrile. In another embodiment, the synthesis be accomplished byperforming the organoamine postgrafting reaction in acetone.

In other embodiments, synthesis methods for selective, efficienttrifunctional nanoporous catalysts for hydrophilic or hydrophobicreactants in the Henry reaction are provided in accordance with theinvention. In these syntheses, two or more organofunctional groups maybe judiciously chosen and co-placed in spatial-isolation and indifferent relative concentrations on the channel walls of mesoporousmaterials, leaving large numbers of residual silanols. In oneembodiment, this was achieved by grafting a mixture of organosilanesonto prior-made mesoporous silica in isopropanol in one-pot. In anotherembodiment, sequential grafting of a first organosilane in isopropanolis performed, followed by a second organosilane in isopropanol ortoluene. This has been demonstrated for 3-aminopropyl groups and asecondary functional group, which included ureidopropyl,3-mercaptopropyl, or methyl groups. While 3-aminopropyl groupsintroduced solid base catalytic sites, the latter groups and theresidual silanol groups on the materials controllably modified thecatalyst's surface to either hydrophilic or hydrophobic, depending uponthe particular grafted second group. By virtue of grafting inisopropanol and the site-isolated multifunctional groups it produced,the resulting materials afforded high catalytic efficiency with nearly100% conversion of various p-substituted benzaldehydes within 15-30minutes in the Henry reaction and tunable, time-dependent selectivitiesto hydrophilic or hydrophobic reactants in mixtures of p-substitutedbenzaldehydes with ratios as high as 7:1. This is a significantachievement compared to examples of previously reported selectivecatalysts, which showed selectivity only for hydrophobic reactants andwith the highest yield of 50% in 24 h and maximum selectivity of2.6:1.0, as reported by Huh, et al. in J. Am. Chem. Soc. 2004, 126,1010-1011, for example. The applicants' synthetic approach is simple,generic, versatile, and can be extended to other reactants and reactionsby judiciously choosing and grafting multiple organic groups insite-isolation on nanoporous materials, as will be describedsubsequently in this specification.

In additional embodiments of the invention, optimized cooperativeacid-base bifunctional mesoporous catalysts for the Henry reaction areprovided. The applicants have discovered that the site-isolation andrelative concentrations of the bifunctional groups can be controlled bysimple, one-step, facile grafting of organoamines on mesoporous silicaat various temperatures using ethanol and toluene as solvents; and thatthe separation distances between the functional groups can be controlledby using shorter and longer organoamines, i.e. grafting organoamines ofspecifically chosen lengths. In accordance with the invention,organomonoamine- and organodiamine-functionalized samples with variousdegrees of site-isolation, relative concentrations of the bifunctionalgroups, and separation distances are provided, as well as a preparationmethod therefor comprising a simple, one-step, facile grafting oforganosilanes on mesoporous silica at various temperatures using ethanoland toluene solvents.

The advantages of these catalysts having spatially distributedorganoamines and silanols was demonstrated in one embodiment bysynthesizing 3-aminopropyl functionalized mesoporous materials. Onecatalyst of the present invention resulted in a four fold increasedcatalytic efficiency or turn-over number for the Henry reaction, ascompared to prior art mesoporous silica catalysts that have beenprepared in toluene in reflux. This catalyst material afforded a 99.4%yield for one example of the Henry reaction within 15 minutes. To thebest of the applicants' knowledge, this is the highest catalyticefficiency of any mesoporous catalyst reported for the Henry reaction.

One aspect of the invention is based on the discovery of severaltechniques for synthesizing catalysts comprised of spatially distributedacid and base functional groups on mesoporous silica. The techniquesenable the provision of selective and highly efficient multifunctionalnanoporous catalysts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by reference to the following drawings,in which like numerals refer to like elements, and in which:

FIG. 1 is a three-dimensional schematic illustration of one exemplarymesoporous material to which the present invention is applicable;

FIG. 2 is an illustration that summarizes the reaction schemes forconverting the mesoporous material of FIG. 1 into certain catalysts ofthe invention;

FIG. 3A is a graph of powder X-ray diffraction patterns of a mesoporoussilicate material MCM-41, one exemplary catalyst AP-E1 of the invention,and two control catalyst samples AP-T1, and AP-T2;

FIG. 3B is a graph of powder X-ray diffraction patterns of a mesoporoussilicate material, the catalyst AP-E1 and the control samples of FIG.2A, and additional catalysts synthesized by postgrafting a lesser amountof 3-aminopropyltrimethoxysilane (APTMS) in toluene and/or in shorterpostgrafting reaction times;

FIG. 4A and FIG. 4B are transmission electron microscopy images of thecatalyst AP-E1;

FIG. 5A is a composite graph of the N₂ adsorption isotherms for theMCM-41, AP-E1, AP-T1, and AP-T2 materials;

FIGS. 5B-5E are the individual isotherms and pore-size distribution datafor the MCM-41, AP-E1, AP-T1, and AP-T2 materials;

FIG. 6A is a graph of the ²⁹Si spectra obtained for the MCM-41, AP-E1,AP-T1, and AP-T2 materials;

FIG. 6B is a graph of the ¹³C spectra obtained for the AP-E1 and AP-T2materials;

FIG. 7 is a graph of the thermogravimetric analyses of the MCM-41,AP-E1, AP-T1, and AP-T2 materials over the range from about 25 to about700° C.;

FIG. 8 is a graph of the efficacy of the catalyst AP-E1 of the inventionand the control catalyst samples AP-T1 and AP-T2 in catalyzing the Henryreaction;

FIG. 9A is an illustration of a possible mechanism for the catalysis ofthe Henry reaction by the applicants' AP-E1 catalyst material;

FIG. 9B is an illustration of a possible mechanism for the catalysis ofthe Henry reaction by the control catalyst materials AP-T1 and AP-T2;

FIGS. 10A and 10B are graphs of the efficacy of catalyst samples thatwere synthesized by decreasing the concentrations of aminorganosilanesand/or decreasing the postgrafting reaction times of the synthesis;

FIG. 11 is an illustration summarizing reaction schemes for converting amesoporous material into certain catalysts, wherein various differenttypes of solvents are used as the reaction medium;

FIG. 12A is a graph of powder X-ray diffraction patterns of certaincatalysts prepared in polar protic solvents;

FIG. 12B is a graph of powder X-ray diffraction patterns of certaincatalysts prepared in dipolar protic solvents or in non-polar solvents;

FIG. 13A is a set of transmission electron microscopy images of theMCM-41 starting material, and catalysts prepared in isopropanol and indimethyl formamide;

FIG. 13B is a set of transmission electron microscopy images of acatalyst prepared in ethyl acetate;

FIGS. 14A-14C are nitrogen gas adsorption isotherms and pore-sizedistribution data for 3-aminopropyl-grafted mesoporous samples graftedin polar protic solvents;

FIGS. 15A-15F are nitrogen gas adsorption isotherms and pore-sizedistribution data for 3-aminopropyl-grafted mesoporous samples graftedin dipolar aprotic solvents;

FIGS. 16A-16B are nitrogen gas adsorption isotherms and pore-sizedistribution data for 3-aminopropyl-grafted mesoporous samples graftedin non-polar solvents;

FIGS. 17A-17C are the respective solid-state ²⁹Si MAS NMR spectra of3-aminopropyl-functionalized samples in polar protic solvents, dipolaraprotic solvents, and non-polar solvents;

FIGS. 18A-18C are the respective solid-state ¹³C CP MAS NMR of3-aminopropyl-functionalized samples in polar protic solvents, dipolaraprotic solvents, and non-polar solvents;

FIGS. 19A-19B are the respective thermogravimetric traces of3-aminopropyl-functionalized samples in polar protic solvents, dipolaraprotic solvents, and non-polar solvents;

FIG. 20 is a graph showing the correlation between the dielectricconstant of reaction medium solvent and the percent of functional groupsgrafted to available sites in the pores of the MCM-41 substrate;

FIG. 21 is a graph of reaction yield versus time for the Henry reactionp-hydroxy benzaldehyde and nitromethane that was catalyzed by3-aminopropyl-functionalized samples prepared in polar protic solvents,dipolar aprotic solvents, and non-polar solvents;

FIG. 22 is a graph of surface area versus percent of functional groupsgrafted to available sites;

FIG. 23 is a graph of % yield in the Henry reaction at 15 minutesreaction time versus catalyst surface area;

FIG. 24 is a graph of % yield in the Henry reaction at 15 minutesreaction time versus percent of functional groups grafted to availablesites;

FIG. 25 is an illustration summarizing reaction schemes for converting amesoporous material into certain catalysts having organoamine functionalgroups wherein the relative proportions of silanol and postgraftedorganoamine are dependent upon the reaction solvent polarity anddielectric constant;

FIG. 26 is an illustration summarizing reaction schemes for converting amesoporous material into certain mesoporous selective catalystscontaining site-isolated 3-aminopropyl groups, many residual silanols,and secondary organic functional groups, including ureidopropyl,3-mercaptopropyl, or methyl groups;

FIG. 27A is a graph of powder X-ray diffraction patterns of certaincatalysts prepared on the mesoporous silicate MCM-41 in accordance withthe reaction scheme of FIG. 26;

FIG. 27B is a graph of powder X-ray diffraction patterns of certaincatalysts prepared on the mesoporous silicate SBA-15;

FIG. 28(A)-(F) are transmission electron microscopy images of (A) MCM-41mesoporous silicate starting material and selected trifunctionalmesoporous catalysts synthesized therefrom, (B) APMP1, (C) APME1, (D)APMP2, (E) APME2 and (F) API1, respectively;

FIG. 29(A)-(D) are transmission electron microscopy images of (A) MCM-41mesoporous silicate starting material and selected trifunctionalmesoporous catalysts synthesized therefrom, (B) API1-SBA, (B) APUD1-SBA,and APME-1, respectively;

FIGS. 30A-30C are nitrogen gas adsorption isotherms of selectedtrifunctional mesoporous catalysts synthesized from MCM-41 mesoporoussilicate starting material;

FIG. 30D is a set of nitrogen gas adsorption isotherms of selectedtrifunctional mesoporous catalysts synthesized from SBA-15 mesoporoussilicate starting material;

FIG. 31A depicts ¹³C CP-MAS solid-state NMR spectra of varioustrifunctional mesoporous catalysts;

FIG. 31B depicts ²⁹Si MAS solid-state NMR spectroscopy of MCM-41, andvarious trifunctional mesoporous catalysts;

FIGS. 32A-32N are a series of reaction time plots (% yield versus timeplots) for the Henry reaction of individual reactants catalyzed byvarious trifunctional mesoporous catalysts synthesized from parentMCM-41 mesoporous silica;

FIGS. 32 a-32 n are a series of plots for corresponding to therespective FIGS. 32A-32N, showing the ratio of % yield versus time forone reactant over another reactant and the time at which the maximumratio of the % yield occurred;

FIGS. 33A-33C are a set of comparative catalysis time plots (% yieldversus reaction time) of the Henry reaction compiled for each reactantp-OH, p-But, and p-Me catalyzed by all the catalysts synthesized fromthe parent MCM-41 mesoporous silica;

FIGS. 34A-34L are a series of reaction time plots (% yield versus timeplots) for the Henry reaction of 1:1 mole mixture of two reactantscatalyzed by various selected trifunctional mesoporous catalystsprepared from parent MCM-41 mesoporous silica;

FIGS. 34 a-34 l are a series of plots for corresponding to therespective FIGS. 34A-34L, showing the ratio of % yield versus time forone reactant over another reactant and the time at which the maximumratio of the % yield occurred;

FIGS. 35A-35E are a series of reaction time plots (% yield versus timeplots) for the Henry reaction of 1:1 mole mixture of two reactantscatalyzed by various selected trifunctional mesoporous catalystsprepared from parent SBA-15 mesoporous silica;

FIGS. 35 a-35 e are a series of plots for corresponding to therespective FIGS. 35A-35E, showing the ratio of % yield versus time forone reactant over another reactant and the time at which the maximumratio of the % yield occurred;

FIG. 36 is a graph of the effect of drying of the trifunctionalmesoporous catalysts in the Henry reaction, as demonstrated by the API1sample, which was dried under ambient condition 1 hour and in an oven at80° C. for 12 hours;

FIG. 37 is a schematic illustration of the applicants' synthesis ofselective, efficient trifunctional mesoporous catalysts containingmultiple site-isolated functional groups for selective catalysis ofeither hydrophilic or hydrophobic reactants in the Henry reaction;

FIG. 38 is an illustration summarizing reaction schemes for convertingthe mesoporous material MCM-41 into catalysts containing variousconcentrations of organomonoamine via grafting ofaminopropyltrimethoxysilane onto MCM-41 in ethanol and toluene atvarious temperatures;

FIG. 39A depicts the powder X-ray diffraction patterns of MCM-41compared with the certain organomonoamine functionalized mesoporouscatalyst samples prepared by grafting in ethanol and toluene;

FIG. 39B depicts the powder X-ray diffraction patterns of MCM-41compared with certain organodiamine functionalized catalyst samples;

FIG. 39C depicts small angle X-ray scattering (SAXS) of MCM-41 comparedwith the certain organomonoamine functionalized mesoporous catalystsamples prepared by grafting in ethanol and toluene;

FIG. 39D depicts small angle X-ray scattering of MCM-41 compared withcertain organodiamine functionalized catalyst samples;

FIG. 40(A)-(F) are transmission electron microscopy images of MCM-41mesoporous silicate starting material, and selected organomonoamine andorganodiamine mesoporous catalysts synthesized therefrom;

FIGS. 41A and 41B are nitrogen gas adsorption isotherms of MCM-41mesoporous silicate starting material, and selected organomonoamine andorganodiamine mesoporous catalysts synthesized therefrom;

FIGS. 41C-4J are the individual isotherms and pore-size distributiondata for the AAP-E1, AAP-T1, AP-EE1, AP-ET1, AP-EE2, AP-ET2, AP-E1A, andAP-E1B materials;

FIG. 42A depicts ¹³C CP-MAS solid-state NMR spectra of MCM-41 andvarious organomonoamine and organodiamine mesoporous catalysts;

FIG. 42B depicts ²⁹Si MAS solid-state NMR spectroscopy of MCM-41 andvarious organomonoamine and organodiamine mesoporous catalysts;

FIG. 42C depicts a comparison of the ²⁹Si CP MAS compared with ²⁹Si MASNMR spectra for the monoamine and diamine functionalized mesoporoussamples;

FIGS. 43A and 43B depict thermogravimetric analyses of the MCM-41 samplecompared with monoamine and diamine functionalized samples grafted inethanol and toluene;

FIGS. 44A and 44B are catalysis time plots of certain monoamine anddiamine functionalized samples grafted in ethanol and toluene;

FIG. 45 is a schematic illustration of the mechanisms and differences ofcooperative catalysis by amines and silanols groups in certain monoamineand diamine functionalized samples grafted in ethanol and toluenesamples in the Henry reaction between p-hydroxybenzaldehyde andnitromethane;

FIGS. 46A and 46B are a schematic illustrations of the graftingfunctionalization of one organoamine functionalized catalyst sample ofthe invention with additional organosilanes in ethanol and toluene,respectively;

FIG. 47 is a temperature dependent catalysis time plot of certainorganodiamine-functionalized mesoporous catalyst materials of theinvention; and

FIG. 48 is a schematic representation of the relative efficiencies incatalysis of the Henry reaction by the applicants' monoamine and diaminefunctionalized mesoporous catalyst samples grafted in ethanol andtoluene.

The present invention will be described in connection with certainpreferred embodiments. However, it will be understood that there is nointent to limit the invention to the embodiments described. On thecontrary, the intent is to cover all alternatives, modifications, andequivalents as may be included within the spirit and scope of theinvention as defined by the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For a general understanding of the present invention, reference is madeto the drawings. In the drawings, like reference numerals have been usedthroughout to designate identical elements. In describing the presentinvention, a variety of terms are used in the description.

As used herein, the term “catalyst” is meant to indicate a substancethat increases the rate of a chemical reaction while not being consumedin the reaction.

As used herein, the term “selective,” when used in reference to acatalyst, is meant to indicate the capability of the catalyst to causethe production of specific products by selectively catalyzing a specificreactant or reaction in a mixture of similarly reactive compounds orfrom competitive reactions. This capability may be the result of thegeometry of the catalyst substrate in combination with the species ofchemical groups grafted to the substrate and/or their density on thesubstrate and/or their locations and/or their relative proportions onthe substrate.

As used herein, the term “mesoporous material” is meant to indicate amaterial containing pores between about 2 and about 50 nanometers acrossthe pore (i.e. in diameter if the pores are substantially circular incross-section).

As used herein, the term “postgrafting” when used in reference to afunctional chemical group and a mesoporous material is meant to indicatethe bonding of that group to the surface of the mesoporous material.

As used herein, the term “turnover number” when used in reference to acatalyst of a chemical reaction is meant to indicate the number of molesof reactant that a mole of catalyst can convert to product beforebecoming inactivated.

As used herein, the term “ambient conditions” when used in reference toa chemical synthesis is meant to indicate the typical conditions in alaboratory, i.e. a temperature of about 20 to 30 degrees Centigrade (°C.) and atmospheric pressure.

As used herein, the term “spatially distributed,” when used in referenceto functional groups attached to the mesopores of a catalyst material,is meant to indicate a density of distribution of the functional groupsthat is less than the maximum possible attainable density ofdistribution. The terms “spatially distributed,” “spatially isolated,”and “site-isolated” are used interchangeably herein.

In accordance with the present invention, multifunctional catalysts areprovided containing spatially distributed acid and base groups graftedto a substrate. Various substrates may be used upon which the acid andbase groups are provided, including but not limited to, e.g., silicamicrospheres or silica gels. A preferred class of substrates having ahigh degree of porosity and a high surface area are mesoporoussubstrates. FIG. 1 is a three-dimensional schematic illustration of oneexemplary mesoporous substrate material to which the present inventionis applicable. Mesoporous material 10 is known in the art as MobileCrystalline Material 41, or MCM-41, which is a silicate material. MCM-41is ordered to some degree, and is comprised of arrays of nonintersecting hexagonal channels or pores, such as pore 12. In FIG. 1,the longitudinal axis of pore 12 is disposed along the z axis. The sixwalls 14A-14F of pore 12 provide the generally hexagonal shape of pore12, and each of walls 14A-14F may form part of the wall of an adjacenthexagonal pore. In the illustration of FIG. 1, the hexagonal poresrepeat in the X-Y plane with longitudinal axes in the Z direction.Portions of these adjacent pores, for example, pores 16 and 18 are alsoshown in FIG. 1. To an approximation, pore 12 has a wall thickness 24equal to the unit cell diameter 26 minus the pore diameter 28.

The walls of the channels are amorphous SiO₂. For the sake of simplicityof illustration, the hydrogen atoms which form the silanol groups on thepore walls are not shown in FIG. 1. In the methods of the presentinvention, certain functional groups, such as the aminopropyl group 20are postgrafted to the walls 14A-14E in controlled and spatiallyisolated arrangements to make the catalysts of the present invention, aswill be explained herein. It is to be understood that although the pore12 and adjacent pores of material 10 appear to be of a relativelyshallow depth, these pores may extend a considerable distance furtheralong the z axis. Additionally such pores are not necessarily disposedstraight along the z axis and may deviate therefrom.

Various embodiment of the invention will be described herein. Ingeneral, selective and efficient multifunctional nanoporous catalystscomprising acid and/or base functional groups that are postgraftedwithin the pores of a mesoporous substrate with controlled spatialdistributions are provided in accordance with the invention.Additionally, synthetic methods for making such catalysts are provided.

Spatially Distributed Organoamine Groups on Mesoporous Silica: GeneralDescription and Examples

In certain embodiments of the invention, catalysts are provided whichare comprised of spatially distributed organoamine groups on mesoporoussilica. Synthesis of these catalysts was achieved by reacting excessaminoorganosilanes in ethanol; or in an alternative embodiment bypostgrafting lower amounts of aminoorganosilanes in toluene for a shortreaction time. Despite the lower number of catalytic sites, theresulting reaction products that have increased cooperative propertiesand higher surface areas gave the most enhanced catalytic properties inexamples of the Henry reaction. The applicants have confirmed that suchone-pot synthetic methods allow the preparation of spatially isolatedbifunctional catalysts, which, to the best of the applicants' knowledge,until now were only achieved through lengthy multi-step, costly methods.In contrast, this scheme of the synthetic methods of the presentinvention is a very simple, one step versatile procedure as compared tothose previously reported procedures of which the applicants are aware.

The following description provides examples of the applicants' catalyststhat are comprised of spatially distributed organoamine groups onmesoporous silica, and their methods of preparation. It is to beunderstood that the instant catalysts described herein are exemplary,and that many other variants are to be construed as being within thescope of the invention. For example, other forms of mesoporous materialsmay be used instead of or in addition to the MCM-41 material, includingbut not limited to SBA-15.

In one embodiment, bifunctional, spatially isolated organoamine andsilanol groups were postgrafted to the mesoporous silicate MCM-41. TheMCM-41 was synthesized as follows: 2.0 g (5.5 mmol)cetyltrimethylammonium bromide (CTAB) was mixed with 480 g (26.7 mmol)of millipore water and 7 mL, 2.0 M NaOH solution. The solution wasstirred for 30 minutes at 80° C. before the addition of 11.3 mL (50.6mmol) tetraethoxysilane into it. The mixture was stirred moderately for2 hours at 80° C. The solution was filtered and the precipitate waswashed with 40 mL millipore water four times, followed by ethanol anddried under air for 4 hours. The CTAB surfactant was extracted bystirring 1 g of the sample in a solution of 0.5 mL of HCl and 150 mL ofethanol at 50° C. for 5 h. The resulting mesoporous material wasfiltered and washed again with millipore water and 40 mL ethanol. Theextracted MCM-41 was then dried under vacuum for 3-4 hours and kept inan oven at 80° C. to remove physisorbed water prior before postgrafting.As used herein, the term “millipore water” is meant to indicate waterthat has been purified to a resistivity of at least 18 megaohms.

The chosen organoamine group was the 3-aminopropyl group. Thepostgrafting was performed by stirring an excess amount of3-aminopropytrimethoxysilane with MCM-41 in ethanol under reflux at 78°C. for 6 hours. The solution was filtered and the precipitate was washedwith dichloromethane (200 mL) and ethanol (500 mL) and then dried in airto produce a first catalyst named and further referred to herein as“AP-E1.” To obtain a first control sample, an excess amount of the sameorganosilane was postgrafted onto MCM-41 in toluene at 78° C. Thesolution was filtered and the precipitate washed as described above. Thefirst control sample is named and further referred to herein as “AP-T1.”To obtain a second control sample, an excess amount of the sameorganosilane was postgrafted onto MCM-41 in refluxing toluene at 112° C.The solution was filtered and the precipitate washed as described above.The second control sample is named and further referred to herein as“AP-T2.” FIG. 2 is an illustration that summarizes the reaction schemesfor converting the mesoporous material of FIG. 1 into AP-E1, AP-T1, andAP-T2. Additionally, Table 1 lists structural information for thesematerials.

TABLE 1 Structural information of MCM-41, AP-E1, AP-T1 and AP-T2. PorePore Wall Surface Volume Unit Cell, a₀, Diameter Thickness Sample Area(m²/g) (cm³/g) (Å)^(a) (Å) (Å)^(b) MCM-41 1030 0.88 44.3 34.1 10.2 AP-E1906 0.71 44.4 31.4 13.0 AP-T1 260 0.20 45.6 31.5 14.1 AP-T2 60 0.07 44.430.6 13.8 ^(a)a_(o) = 2d₁₀₀/3^(1/2) (Å) for 2-D hexagonally orderedmaterials ^(b)Wall thickness = Unit Cell − Pore Diameter.

Alternative postgrafting synthesis methods to produce aminopropylfunctionalized mesoporous materials with spatially isolated aminopropyland silanol groups were also performed. Samples having catalyticproperties similar to those of AP-E1 were prepared in toluene bycarefully controlling the synthesis conditions. Several samples weresynthesized by decreasing the concentrations of aminorganosilanes and/ordecreasing the postgrafting reaction times. Table 2 lists these samplesC-I, along with additional samples of AP-E1 (A) and AP-T1 (B).

TABLE 2 Synthesis, composition and catalytic properties of mesoporouscatalysts with spatially isolated organoamine groups synthesized bypostgrafting a lesser amount of 3-aminopropyltrimethoxysilane (APTMS) intoluene and/or in shorter postgrafting reaction times. Weight loss % %Time (min) Postgrafting (%) Conversion Conversion for 100% SampleSolvent APTMS Time (hr)^(a) (100-600° C.)^(b) in 12 min in 25 minConversion A Ethanol 3.68 mmol 6 11.2 80 100 16 (AP-E1) (Excess) BToluene 3.68 mmol 6 13.2 25 50 54 (AP-T1) (Excess) C Toluene 3.68 mmol 116.1 22 45 74^(c) (Excess) D Toluene 1.21 mmol 6 13.5 29 59 42^(c) E^(d)Toluene 1.21 mmol 1 14.5 89 100 15 F Toluene 0.92 mmol 6 15.4 49 8533^(c) G Toluene 0.92 mmol 1 14.2 26 55 38^(c) H Ethanol 0.92 mmol 611.0 66 100 22 I Ethanol 1.21 mmol 1 10.5 65 100 22 ^(a)The postgraftingtemperature was set to be 78° C. for all the samples. ^(b)The weightloss corresponds to the loss of organoamine groups and loss of water dueto condensation of silanol groups. ^(c)Obtained by extrapolation of thegraph (not shown) of thermogravimetric data for the sample. ^(d)Thissample showed comparable high catalytic efficiency as postgrafted samplein ethanol (AP-E1).

By way of example, sample E of Table 2 was synthesized by stirring 500mg, pre-dried MCM-41 in 0.27 g (1.21 mmol) of3-aminopropyltrimethoxysilane (APTMS) in 250 mL toluene at about 78° C.for 1 hr. The solution was filtered and the precipitate was washed withdichloromethane (200 mL) and ethanol (500 mL) and then dried in air.Similarly, other samples including the original parent materialsinvestigated (sample A, AP-E1, and sample B, AP-T1) were alsosynthesized again as control samples. All of these samples were preparedat 78° C. Their efficacy in the catalysis of a Henry reaction was alsoinvestigated. The results are compiled in Table 2 and FIGS. 10A and 10Band will be described subsequently herein.

The materials of Table 1 and Table 2 were characterized by a variety ofanalytical instruments. A brief description of the individual analyticaltechniques will be provided here, followed by a summary of the data andresults of each technique.

Powder X-ray diffraction (XRD) measurements were made using a Scintagpowder diffractometer. FIG. 3A depicts the powder X-ray diffractionpatterns of MCM-41 and the organoamine functionalized catalyst samplesAP-E1, AP-T1, and AP-T2. FIG. 3B is a graph of powder X-ray diffractionpatterns of the materials of FIG. 3A, as well as additional catalysts ofthe invention.

Transmission electron microscopy (TEM) was performed using a JEOL 2010instrument. FIG. 4A and FIG. 4B are transmission electron microscopyimages of catalyst AP-E1 at two different scales of magnification.

Nitrogen (N₂) gas adsorption measurements were obtained with aMicromeritics ASAP 2020 volumetric adsorption analyzer at 77 Kelvin.Prior to the measurements, the samples were outgassed at 160° C. forabout 4 hours under vacuum, or until the pressure reached less than 6 μmHg. FIG. 5A is a composite graph of the N₂ adsorption isotherms for theMCM-41, AP-E1, AP-T1, and AP-T2 materials, and FIGS. 5B-5E are theindividual isotherms for the materials. The respective correspondingpore size distributions for each sample are also shown in these Figures.

Solid-state ²⁹Si MAS, ²⁹Si CP-MAS and ¹³C CP-MAS NMR spectra of thematerials were measured with a 300 MHz Bruker Avance NMR spectrometer.(“CP” refers to “cross polarization,” and “MAS” refers to “magic anglespinning.” Both terms are well known in Nuclear Magnetic Resonancespectroscopy art.) FIG. 6A shows the ²⁹Si spectra obtained for the foursamples, and FIG. 6B shows the ¹³C spectra obtained for the AP-E1 andAP-T2 materials.

Thermogravimetric analysis (TGA) was carried out with a Q-500Quantachrome instrument manufactured and sold by TA-Instruments. As iswell known to those skilled in the art, TGA is a type of testing that isperformed on samples to determine changes in weight in relation tochange in temperature. FIG. 7 is a graph of the thermogravimetricanalyses of the MCM-41, AP-E1, AP-T1, and AP-T2 materials over the rangefrom about 25 to about 700° C.

Turning now to the results of these material analyses, and referringfirst to FIG. 3A, the table inset shows d₁₀₀ and unit cell (a_(o))values of the samples, wherein a_(o)=2d₁₀₀/3^(1/2) (∈) for 2-Dhexagonally ordered materials. The XRD patterns of all the samplesshowed a sharp peak corresponding to (100) peak as well as at least twomore Bragg reflections corresponding to (110) and (200) peaks indicatingthat the materials have highly hexagonally ordered mesostructures, whichremained intact during postgrafting. The peaks were indexed to give unitcells sizes of about 4.4-4.5 nanometers, which barely changed duringpostgrafting.

Referring to FIG. 3B and Table 2, all of the samples showed well orderedmesoporous structures. It is worth noting however that, samplespostgrafted in ethanol (for instance, A and H) showed slightly moreintense Bragg reflections compared to samples grafted in toluene for thesame period of time at the same temperature (B and F). This clearlyindicates the higher organoamine grafting in the channels of tolueneproduct and the lower electron contrast between the mesoporous channelsand walls. The XRD pattern also reveals that samples grafted withshorter postgrafting times or with more amount of organosilane showedslightly more intense peaks compared to samples postgrafted with longertime or with less amount of organosilane.

Referring to the TEM images of catalyst AP-E1 of FIG. 4A and FIG. 4B,the dimensional scales of these images are indicated in the respectivelower right corners. Other TEM images (not shown) of the materialsbefore postgrafting (i.e. starting material MCM-41) and afterpostgrafting (i.e. various catalyst product samples) also showedwell-ordered mesoporous structures. These images showed clear channelstructures similar to the channels 22 in the catalyst sample shown inFIG. 13B.

Referring to FIGS. 5A-5E, the gas adsorption measurements of all thematerials exhibited BDDT (Brunauer, Deming, Deming, and Teller) Type IVisotherms, which are characteristic of mesoporous materials.Furthermore, their BET (Brunauer-Emmett-Teller) surface areas rangebetween 1,030-1,060 m²/g depending on grafting density, while their BJH(Barrett-Joyner-Halenda) pore size distributions are monodisperse.

Referring in particular to the individual pore size distribution plotsof FIGS. 5B-5E, it can be seen that the distributions indicatemonodisperse pore diameters, and that the capillary condensation stepand the pore volume decreases in the order of MCM-41>AP-E1>AP-T1>AP-T2.This result is consistent with more grafting of organoamine groups inthe mesoporous structures. The decrease of surface areas and porevolumes upon grafting of organic groups is previously known. Despite theobserved significant decrease in pore volume and surface area, AP-T2 hasstill a well-ordered mesostructure as shown by its Type IV isotherm(FIG. 5E) and its intense peaks in its X-ray diffraction pattern (FIG.3A).

Referring to FIG. 6A, by integration of the ²⁹Si MAS spectra, thecomposition of the mesoporous materials MCM-41, AP-E1, AP-T1, and AP-T2and the mmol NH₂/g for each material were obtained. In each of thefollowing paragraphs, the numbers in the bracket indicate % silica and %organosilica for each material that were obtained by integrating the²⁹Si MAS spectra.

The composition of the MCM-41 can be represented as:

{(SiO₂)_(Q4)[SiO_(1.5)(OH)]_(Q3)[SiO(OH)₂]_(Q2)}

The compositions of AP-E1, AP-T1, and AP-T2 can be represented as:

{(SiO₂)_(Q4)[SiO_(1.5)(OH)]_(Q3)[SiO(OH)₂]_(Q2)}{[SiO_(1.5)C₃H₈N)]_(T3)[SiO(OH)C₃H₈N]_(T2)[SiO_(0.5)(OH)₂C₃H₈N]_(T1)}

From the integration values:

For MCM-41:

{(SiO₂)_(Q4)[SiO_(1.5)(OH)]_(Q3)[SiO(OH)₂]_(Q1)}═{(SiO₂)_(0.59)[SiO_(1.5)(OH)]_(0.41)[SiO(OH)₂]₀═{(SiO₂)_(0.59)[SiO_(1.5)(OH)]_(0.41)}

For AP-E1:

{(SiO₂)Q₄[SiO_(1.5)(OH)]_(Q3)[SiO(OH)₂]Q₁}{[SiO_(1.5)C₃H₈N)]_(T3)[SiO(OH)C₃H₈N]_(T2)[SiO_(0.5)(OH)₂C₃H₈N]_(T1)}═{(SiO₂)_(0.57)[SiO_(1.5)(OH)]_(0.32)[SiO(OH)₂]_(0.02)}{[SiO_(1.5)C₃H₈N)]_(0.04)[SiO(OH)C₃H₈N]_(0.04)[SiO_(0.5)(OH)₂C₃H₈N]₀}

From the above, the mmol NH₂/g sample was calculated to be 1.32 mmolNH₂/g.

For AP-T1:

{(SiO₂)_(0.47)[SiO_(1.5)(OH)]_(0.16)[SiO(OH)₂]_(0.07)}{[SiO_(1.5)C₃H₈N)]_(0.23)[SiO(OH)C₃H₈N]_(0.11)[SiO_(0.5)(OH)₂C₃H₈N]_(0.02)}

From the above, the mmol NH₂/g sample was calculated to be: 4.1 mmolNH₂/g.

For AP-T2:

{(SiO₂)_(0.57)[SiO_(1.5)(OH)]_(0.08)[SiO(OH)₂]_(0.01)}{[SiO_(1.5)C₃H₈N)]_(0.24)[SiO_(1.5)C₃H₈N]_(0.08)[SiO_(0.5)(OH)₂C₃H₈N]_(0.02)}

From the above, the mmol NH₂/g sample was calculated to be: 4.3 mmolNH₂/g.

Referring to FIG. 7, the thermogravimetric traces for the MCM-41, AP-E1,AP-T1, and AP-T2 materials indicated a weight loss before 100° C. in allthe samples due to the loss of physisorbed water. However, the weightloss of the samples between 100-600° C., which corresponds to the lossof organoamine groups and some condensed water, showed a trend. TheAP-E1 showed the lowest weight loss followed by AP-T1 and then AP-T2;i.e. 10.7, 14.8 and 16.8%, respectively. Considering the removal ofsilanol groups from the materials during postgrafting, which is thehighest in AP-T2, and which therefore results in the lowest weight lossdue to condensation of water on TGA traces, the applicants believe thatthese weight loss differences due to the organoamine between 100-600° C.for AP-E1, AP-T1 and AP-T2 are more significant.

These results were further corroborated with the solid-state NMRspectroscopy results shown in FIGS. 6A and 6B and described previouslyherein. The ²⁹Si MAS NMR of FIG. 6A qualitatively and quantitativelyconfirmed the presence of the highest organoamine groups in AP-T2 (4.3mmol/g), followed by AP-T1 (4.1 mmol/g), and then AP-E1 (1.3 mmol/g).Similarly, the ¹³C CP-MAS NMR of FIG. 5B showed peaks corresponding toaminopropyl groups at 43.1, 24.7, and 8.4 ppm after postgrafting. Theintensities of these peaks were higher for AP-T2, followed by AP-T1, andAP-E1, consistent with the TGA and ²⁹Si MAS NMR results. Both the TGAand solid-state NMR results have confirmed AP-E1 to have a lesser numberof organoamine groups and more silanols, that are likely to be spatiallydistributed, compared to AP-T1 and AP-T2, which have densely populatedorganoamines and fewer silanols.

Referring again to FIG. 2, the lesser amount of aminopropyl groupspostgrafted to a pore wall of the AP-E1 material as compared to a porewall of AP-T1 or AP-T2 is illustrated qualitatively. Accordingly, theaminopropyl groups are spatially distributed less densely in the poresof AP-E1. The significance of this discovery will be explainedsubsequently herein.

In order to demonstrate the usefulness of the bifunctional materialswith spatially isolated organoamine and silanol groups, the applicantshave performed the Henry reaction using the materials A-I of Table 2 ascatalysts. In general, the Henry reaction is an aldol type reactionbetween an aldehyde and nitromethane. The nucleophilic addition step isbase catalyzed and may be followed by an elimination reaction withremoval of water when an acidic alpha proton is present. The reactionproduct is a beta-hydroxy nitro-compound or a nitroethylene compound.

Many organoamine functionalized mesoporous materials synthesized inreflux in toluene are reported to catalyze the Henry reaction. However,to the best of the applicants' knowledge, the highest yield andturnover-number (TON) values reported to date with such samples havebeen 96% yield in 1 hr reaction time with 50 mg catalyst and 2.5 mmol ofreactant, as disclosed by Demicheli et al. in Tetrahedron Lett. 2001,42, 2401-2403; and Choudary, et al in J. Mol. Catal. A 1999, 142,361-365.

In the present application, the Henry reaction between p-hydroxybenzaldehyde and nitromethane at 90° C. was carried out, resulting inthe formation of nitrostyrene. Typically, 20 mg of a particularaminofunctionalized mesoporous sample was added into a mixture of 122 mg(1 mmol) p-hydroxybenzaldehyde and 10 mL of nitromethane. The reactionmixture was stirred at 90° C. under nitrogen and aliquots of thereaction product were taken with a filter syringe and characterized bysolution ¹H NMR spectroscopy and GC-MS over the course of the reactions.The percent yield and conversion were determined by using ¹H NMR spectrameasured in deutrated acetone.

FIG. 8 is a graph of the efficacy of the resulting catalyst AP-E1 of theinvention and the control catalyst samples AP-T1 and AP-T2 in catalyzingthis Henry reaction. Performing the reaction with AP-E1 as a catalystunexpectedly gave a yield of 99.4% in about 15 minutes. In contrast, thesame amounts of AP-T1 and AP-T2 afforded yields of 52.4 and 8.4%,respectively, in 15 minutes. This is at least a two-fold increase inyield. A four-fold increase in turn-over-number for AP-E1 compared toAP-T1 and AP-T2 was also observed. To the best of the applicants'knowledge, it is the highest efficiency compared to any mesoporouscatalyst reported in the literature for the Henry reaction. Theseresults are unexpected, given the fact that AP-E1 has less organoaminegroups per unit mass than both AP-T1 and AP-T2, and considering thatmesostructures in all the samples remained intact as shown by XRD andTEM.

Without wishing to be bound to any particular theory, the applicantsbelieve that the enhanced catalytic efficiency by AP-E1 compared toAP-T1 and AP-T2 may be due to two reasons:

1. The higher number of silanols in AP-E1, as compared to the materialsAP-T1 or AP-T2, can activate the carbonyl group of benzaldehyde toundergo the nitroaldol reaction more efficiently. The correspondingreaction mechanisms for AP-E1, and AP-T1 or AP-T2, are illustrated inFIGS. 9A and 9B, respectively. Referring in particular to FIG. 9A, theapplicants believe that the significant number of spatially isolatedsilanol groups present in AP-E1 activates the carbonyl group ofbenzaldehyde for nucleophilic attack.

2. The higher surface area of AP-E1 due to its low organoamine graftingdensity compared to AP-T1 and AP-T2 may also have contributed to thedifferences in catalytic efficiency.

Similar studies of postgrafting organodiamine groups that the applicantshave conducted using ethanol and toluene also showed increasedefficiency for samples synthesized in ethanol compared to correspondingsamples synthesized and grafted in toluene. The postgrafting of theremaining silanols of the ethanol product (or AP-E1) with more organicgroups using toluene resulted in significant reduction in catalyticefficiency, further confirming the importance of spatially isolatedorganoamine and silanols for increased efficiency. Detailed synthesis ofthese materials and their catalytic properties are describedsubsequently in this specification.

Again, without wishing to be bound to any particular theory, theapplicants hypothesize that postgrafting of spatially distributedorganoamines with ethanol occurs because of the competition for theaminoorganosilane by ethanol (a polar protic solvent having a dielectricconstant=24 D), and the hydrophilic surface silanols. Because of theabsence of hydrogen bonding between the organoamines and toluene (anonpolar solvent having a dielectric constant=2.4 D), theaminoorganosilanes aggregate and preferentially interact with thesurface silanols. Aggregation of aminoorganosilanes in toluene has beenpreviously proposed to cause grafting of very densely populated organicgroups by Hicks et al. in Chem. Mater. 2006, 18, 5022-5032.

However, by lowering the concentration of aminoorganosilane andshortening the reaction times, the applicants have also synthesizedsimilar site isolated samples that have efficient catalytic propertiesin toluene at lower temperature. The synthesis and the catalyticperformance of these site isolated samples C-I are summarized in Table2. Additionally, FIGS. 10A and 10B graphically show the efficacy ofthese catalyst samples C-I, along with samples A (AP-E1) and B (AP-T1)for comparison. It can be seen that the best result was achieved bysample E, in which the concentration of aminoorganosilane was reduced to1.21 mmol, and the reaction time was shortened to one hour.

In summary, most of the prior art grafting of organosilanes has beenperformed in non-polar solvents, mainly toluene. In one embodiment, theapplicants have synthesized organic functionalized mesoporous materialsby grafting organosilanes in a polar solvent, ethanol. Although theapplicants' approach resulted in less numbers of immobilized organicgroups compared to the corresponding grafting in toluene, it producedmaterials with better structures such as higher surface area andsite-isolated organocatalytic sites and consequently, much improvedcatalytic properties.

Despite this successful strategy, to the best the applicants' knowledge,the grafting of organosilanes in many other polar and non-polar solventswith different dielectric constants and the correlations between thesolvents' properties and the structures and catalytic properties of theresulting materials have not been systematically investigated. Theapplicants have performed such an investigation, resulting in furtherembodiments of the invention which are described in the immediatelyfollowing section of this specification.

Improvements in Grafting Spatially Distributed Organoamine Groups onMesoporous Silica by Optimal Solvent Selection: General Description andExamples

In performing this investigation, the applicants have discovered ageneric correlation between the properties of solvents used for graftingand the percentages of grafted organic groups, the structures of theresulting materials, and their catalytic properties. The investigationwas carried out by grafting 3-aminopropyl group, which is among the mostcommon types of organic groups to be grafted onto mesoporous materials,under reflux in various polar protic, polar aprotic, and non-polarsolvents. FIG. 11 is an illustration summarizing reaction schemes forconverting mesoporous material into catalysts, wherein these differenttypes of solvents are used as the reaction medium. Reactions performedwith polar protic solvents produce catalyst products 102, reactionsperformed with dipolar aprotic solvents produce catalyst products 104,and reactions performed with nonpolar solvents produce catalyst products106. The percentages of grafted organic groups, structures, andcatalytic properties of these products will be described subsequentlyherein.

In particular, the applicants have discovered correlations between thepolarity and dielectric constants of solvents used for grafting3-aminopropyltrimethoxysilane, and the concentration of grafted organicgroups, the degree of site-isolation of the 3-aminopropyl functionalgroups and the catalytic properties of the resulting materials for theHenry reaction. We have observed that polar protic solvents with lowdielectric constants used as the grafting reaction medium result insmall concentrations of grafted organic groups and higher surface areasbut more efficient catalytic properties. In contrast, the use of dipolarprotic solvent or non-polar solvent media result in a range of graftingconcentrations of organic functional groups and lower surface areas, aswell as a range of catalytic properties from “poor” to “efficient,”which will be further quantified herein. These differences were furtherfound to be strongly dependent on the dielectric constant of thesolvents. Solvents that have higher dielectric constants were found todecrease the grafting density. Without wishing to be bound to aparticular theory, the applicants believe that this phenomenon maypossibly be due to the increased Coulombs interactive force between theprotonated aminopropylsilane cation and deprotonated silianol anions.

In this solvent medium investigation, MCM-41 was used as the mesoporoussilica substrate material. The MCM-41 was synthesized and kept in anoven to remove most of its physisorbed water prior to grafting, asdescribed previously herein. The postgrafting reactions were alsoperformed in a manner similar to that described previously herein.Briefly, 3-aminopropyltrimethoxysilane was refluxed with parentmesoporous silica (MCM-41) in the particular polar protic, dipolaraprotic, or non-polar solvent under nitrogen for 6 hours. The relativepopulations of the 3-aminopropyl group and the structures and thecatalytic properties of the materials for the Henry (nitroaldol)reaction were then investigated. The techniques of powder x-raydiffraction, transmission electron microscopy, nitrogen gas adsorption,solid state ²⁹Si MAS, ²⁹Si CP-MAS and ¹³C CP-MAS NMR, andthermogravimetric analysis were used to characterize the samples asdescribed previously. Details of these analytical techniques will thusnot be repeated here; instead, only the results will be presented.

FIG. 12A is a graph of powder X-ray diffraction patterns of catalystsprepared in polar protic solvents; and FIG. 12B is a graph of powderX-ray diffraction patterns of catalysts prepared in dipolar proticsolvents or in non-polar solvents. FIG. 13A is a set of transmissionelectron microscopy images of the MCM-41 starting material, andcatalysts prepared in isopropanol and in dimethylformamide; and FIG. 13Bis a transmission electron microscopy image of a catalyst prepared inethyl acetate. N₂ gas adsorption isotherms and pore-size distributiondata of the parent MCM-41 are shown in FIG. 5B. The corresponding datafor the 3-aminopropyl-grafted mesoporous samples grafted in varioussolvents are shown in FIGS. 14A-14C (polar protic solvents), FIGS.15A-15F (dipolar aprotic solvents), and FIGS. 16A-16B (non-polarsolvents).

The transmission electron microscopy (TEM) images and the X-raydiffraction (XRD) patterns of the samples indicated that all thefunctionalized samples had highly ordered mesostructures with unit celldimensions of about 43 Å. Mesopore channels 22 are particularly visiblein the TEM image for the sample synthesized in ethyl acetate (FIG. 13B).The TEM and XRD also revealed that grafting of the MCM-41 sample invarious polar, dipolar, and non-polar solvents did not cause majorstructural difference between the samples and when compared to MCM-41.This was further corroborated by N₂ gas adsorption data, which showedmonodisperse pore size distributions and Type-IV isotherms for all thesamples, which are indicative of mesoporous structures. However, thesurface areas of the materials varied from 150-900 m²/g while theaverage pore sizes varied between 28 to 35 Å depending on the solventused or the percentage of organofunctional groups grafted. Thestructural data of the MCM-41 starting material and the functionalizedsamples of this investigation are shown in Table 3.

TABLE 3 Structural data of MCM-41 and 3-aminopropyl-functionalizedmesoporous materials grafted in various solvents. Surface PoreDielectric Area Volume Unit Cell, a₀, Pore Diameter Wall ThicknessSample Constant (m²/g) (cm³/g) (Å)^(a) (Å) (Å)^(b) Parent Sample MCM-41— 982 ((±6) 0.81 44.3 33.8 10.5 Polar Solvents Isopropanol 18 902 (±7)0.78 44.5 31.2 13.3 Ethanol 24 905 (±3) 0.71 44.4 31.4 13.0 Methanol 33864 (±3) 0.71 44.5 31.2 13.3 Dipolar, Aprotic Solvents Ethyl 6.0 153(±4) 0.14 45.4 34.9 10.5 acetate THF 7.5 293 (±7) 44.3 30.1 14.2 Acetone21 617 (±7) 0.50 44.3 30.0 14.3 DMF 38 501 (±11) 0.27 44.6 29.4 15.2DMSO 47 451 (±11) 44.4 31.1 13.3 Acetonitrile 82 618 (±6) 0.46 44.1 28.815.3 Non-polar Solvents Toluene 2.4 259 (±5) 0.20 45.6 31.5 14.1Chloroform 4.8 628 (±7) 0.49 44.5 29.8 14.7 ^(a)a₀ = 2d₁₀₀/3^(1/2) (Å)for 2-D hexagonally ordered materials ^(b)Wall thickness is defined asUnit Cell Diameter − Pore Diameter.

FIGS. 17A-17C are the respective solid-state ²⁹Si MAS NMR spectra of3-aminopropyl-functionalized samples in polar protic solvents, dipolaraprotic solvents, and non-polar solvents; FIGS. 18A-18C are therespective solid-state ¹³C CP MAS NMR of 3-aminopropyl-functionalizedsamples in polar protic solvents, dipolar aprotic solvents, andnon-polar solvents; and FIGS. 19A-19B are the respectivethermogravimetric traces of 3-aminopropyl-functionalized samples inpolar protic solvents, dipolar aprotic solvents, and non-polar solvents.Additionally, Table 4 summarizes the results of the grating syntheses inthe various solvents.

TABLE 4 Results of grafting synthesis of 3-aminopropyl-functionalizedmesoporous materials in various solvents. Dielectric Surface EfficiencyConstant Wt. % Area (Yield in Sample (D) % T^(a) (100-600° C.) (m²/g) 12min)^(b) Polar Solvents Isopropanol 18 11.7 12.0 902 (±7) 97.5% Ethanol24 7.2 12.5 905 (±3) 95.0% Methanol 33 6.8 8.0 864 (±3) 91.5% Dipolar,Aprotic Solvents Ethyl 6.0 24.0 18.5 153 (±4) 28.0% acetate THF 7.5 17.115.4 293 (±7) 38.0% Acetone 21 16.6 13.5 617 (±7) 91.5% DMF 38 20.4 17.5501 (±11) 59.0% DMSO 47 17.8 13.8 451 (±11) 93.4% Acetonitrile 82 18.614.0 618 (±6) 95.8% Non-polar Solvents Toluene 2.4 23.4 17.8 259 (±5)41.0% Chloroform 4.8 22.0 15.2 628 (±7) 85.0% ^(a)% T is the percentageof aminopropylsilica {(OH)_(x)O_(y)Si—(CH₂)₃NH₂} obtained from theintegration of peaks in the ²⁹Si MAS NMR spectra. ^(b)The yield of thereaction between p-hydroxy benzaldehyde and nitromethane at 15 min ofreaction time for 20 mg catalyst. THF: tetrahydrofuran; DMF:N,N-dimethylformamide; and DMSO: dimethylsulphoxide.

The percentage of the grafted 3-aminopropyl groups (column 3 in Table 4)was determined from the weight loss in the range of 150-600° C. onthermogravimetric analysis (TGA) traces (FIGS. 19A-19B) and byquantitative solid-state ²⁹Si MAS NMR spectroscopy (FIGS. 17A-17C). Theresults indicated that samples grafted in polar, protic solvents to havelower percentages of 3-aminopropyl groups than those grafted innon-polar and dipolar, aprotic solvents. Without wishing to be bound toany particular theory, the applicants believe that this is most likelydue to the strong hydrogen bonding between the aminorganosilane and thepolar solvents, which lowers the tendency of aminorganosilane to go tothe hydrophilic silanol groups to graft. The percentage of the3-aminopropyl was also correlated with the solvent's dielectric constantas shown in FIG. 20.

For example, for polar, protic solvents, the trend in the percentage oforganic group was isopropanol>ethanol>methanol, indicating that solventswith lower dielectric constant grafted more organic groups. A similardielectric constant dependent trend was exhibited by a series ofdiprotic, apolar solvents. Generally, the increase in dielectricconstant of the solvent resulted in less number of aminopropyl groups(but higher surface areas), which the applicants believe is most likelydue to the lower Coulomb's interactive force (F=kq₁q₂/er²) betweenprotonated aminopropylsilane cation and deprotonated surface silanolanion. The Coulomb's interactive force is inversely proportional withthe dielectric constant of the solvent as expressed by Coulomb's law.

Referring in particular to FIGS. 17A and 19A, the applicants alsobelieve that the observed ethoxy and methoxy groups in samples graftedin methanol and ethanol in indicate possible exchange of alkoxides fromthe solvents with the surface silanol groups (Si—OH+EtOH

Si—OEt+H₂O) and the presence of some residual unhydrolyzed alkoxides.The increased weight loss in the TGA (in the range of 150-600° C.) forthese samples on the TGA traces could also be due to the additional lossof these alkoxide groups.

In this solvent medium investigation, the Henry reaction betweenp-hydroxy benzaldehyde and nitromethane at 90° C. was carried out,resulting in the formation of nitrostyrene as described previouslyherein. The results of this reaction study for the various solvents andrelated data of Table 4 are shown in FIGS. 21-24. FIG. 21 is a graph ofreaction yield versus time for this reaction that was carried out in thevarious solvent media. FIG. 22 is a graph of surface area versus percentof functional groups grafted to available sites. FIG. 23 is a graph of %yield in the Henry reaction at 15 minutes reaction time versus catalystsurface area, and FIG. 24 is a graph of % yield in the Henry reaction at15 minutes reaction time versus percent of functional groups grafted toavailable sites.

The efficiency of the 3-aminopropyl-functionalized materials to catalyzethis Henry reaction showed an unexpected trend. Referring in particularto FIG. 21 and Table 4, it can be seen that for the polar, proticsolvents used for grafting, the catalytic efficiency of the materialsdecreased in the order of isopropanol>ethanol>methanol. This isinconsistent with the concentrations of grafted organoamines.Unprecedented higher catalytic efficiency by a sample grafted inisopropanol was obtained, even compared to the catalyst AP-E1 preparedin ethanol and previously described in this specification.

Isopropanol resulted in a slightly higher number of grafted organoaminescompared to ethanol and methanol. Upon grafting in dipolar, aproticsolvents, the concentration of organoamines increased, but theefficiency decreased except for acetonitrile. Further, the samplegrafted in acetone, which likely formed imines as indicated by theobvious yellowish color of the reaction solution, showed anexceptionally higher yield in the series of solvents as well.

The applicants have further found that samples that have higher surfaceareas also tend to have higher catalytic efficiency (FIG. 23). However,the differences in surface areas alone do not fully explain the observeddifferences in the catalytic efficiency. For instance, chloroform showedhigher surface area than acetonitrile but the latter showed morecatalytic efficiency.

These results reveal that a combination of surface area andsite-isolation of the catalytic sites played roles for observeddifferences in catalytic efficiency. This work also demonstrates thatoptimum grafting of catalytic sites and enhanced catalytic efficiencycan be achieved by proper choice of grafting solvents. Referring to FIG.25, the relative amount n of silanol groups and the relative amount m oforganoamine groups that are present in the mesoporous catalyst materialmay be optimized to produce a catalyst of high efficiency. Based uponthe applicants' discoveries, this may be accomplished in one embodimentby providing postgrafting of organoamine groups at a density of betweenabout 6 and about 15 percent of the available sites. In anotherembodiment, this may be accomplished by performing the organoaminepostgrafting reaction in a polar aprotic solvent. The solvent may be alow molecular weight alcohol, such as methanol, ethanol, and preferablyisopropanol. In another embodiment, this may be accomplished byperforming the organoamine postgrafting reaction in acetonitrile. Inanother embodiment, this may be accomplished by performing theorganoamine postgrafting reaction in acetone.

Selective, Efficient Trifunctional Nanoporous Catalysts Via Co-Placementof Site-Isolated Multifunctional Groups on Mesoporous Materials

A synthetic strategy to selective and efficient trifunctional mesoporouscatalysts for various p-substituted hydrophilic or hydrophobic reactantsin the Henry reaction has been discovered. The synthesis involves thegrafting of two site-isolated organofunctional groups simultaneously inpolar solvents or by sequential grafting of one group in a polar solventfollowed by another in a polar or non-polar solvent. These syntheticconditions allowed the co-placement of two different organic groups in asite-isolated arrangement, along with many residual silanols on thesurface of the nanoporous materials.

The applicants have demonstrated this for 3-aminopropyl groups and asecondary functional group, which included ureidopropyl,3-mercaptopropyl, or methyl groups. By judicious choice of the types andthe relative concentrations of the two functional groups and theresidual silanols in the materials, the selective catalytic propertiesfor hydrophilic or hydrophobic reactants and the efficiency of thecatalysts were tuned. Selectivities for the hydrophilic and hydrophobicreactants, with values as high as 7:1, were achieved by simply changingthe loading of secondary organic groups in the materials. Furthermore,the site-isolation grafting of these multiple functional groups enableda high catalytic efficiency, with typical values of nearly 100%conversion in less than 30 minutes. To the best the applicants'knowledge, there are no examples in the literature of a singlefunctionalized nanoporous material with selectivity for both hydrophilicand hydrophobic reactants over various time intervals with such highefficiency and short conversion time.

The synthesis of the trifunctional catalysts was achieved by extendingthe synthetic approach previously described herein, in which anefficient bifunctional catalyst for the Henry reaction is producedcontaining a single type of site-isolated organocatalytic groups. Inthis invention, the co-placement of judiciously chosen multiplesite-isolated functional groups in controlled number is achieved bygrafting multiple organosilanes in polar solvents to produce not onlyefficient but also selective catalysts both for hydrophobic andhydrophilic reactants. This has been demonstrated for 3-aminopropylorganocatalytic groups and a secondary functional group, which includedureidopropyl, 3-mercaptopropyl, or methyl groups, which allowedmodifying the materials' surface properties. Furthermore, many residualsilanol groups remained on the materials' surface due to polar solventbeing used for the grafting. The applicants have discovered that havingthe silanol groups has proven to be important in order to maximizecatalytic efficiency.

The catalytic properties of the resulting materials were investigated inthe Henry reaction between various p-substituted benzaldehydes andnitromethane, for each reactant separately, or in 1:1 mole ratio ofreactant mixtures. The reactants included p-hydroxybenzaldehyde (p-OH),p-butoxybenzaldehyde (p-But), p-methylbenzaldehyde (p-Me), andp-methoxybenzaldehyde (p-MeO). The samples containing site-isolated3-aminopropyl groups alone or with ureidopropyl groups preferentiallycatalyzed a hydrophilic reactant, p-hydroxybenzaldehyde, with aselectivity of 1.6 to 2.8 times over a relatively more hydrophobicreactant p-butoxybenzaldehyde. However, upon introduction of hydrophobicorganic groups such as 3-mercaptopropyl and methyl groups along with the3-aminopropyl groups, the selectivity of the catalysts to hydrophilicbenzaldehydes decreased relative to the hydrophobic benzaldehydes. Bysystematic grafting of site-isolated 3:1 and 9:1 mol ratios ofmethyl:aminopropyl groups, the selective catalytic property for thehydrophobic reactants increased to as high as 4:1. It is especiallynoteworthy that these selectivities were accompanied by an extremelysmall reaction time (typically 15-30 minutes) and relatively high %conversion (very nearly 100% in many cases). This is in contrast topreviously reported results, such as the work reported by Huh et al. inJ. Am. Chem. Soc. 2004, 126, 1010-1011, where only a maximum of 50%yield over 24 hrs was achieved and selectivity only for hydrophobicreagents was possible.

Furthermore, the applicants have performed a study of % yield versustime plots to understand the kinetic progress of the reaction for bothindividual reactants and for various combination of a mixture of tworeactants by mesoporous catalysts. It has been observed that selectivityfor hydrophilic or hydrophobic reactants by a single catalyst variedwith time, with maximum selectivity reaching at an intermediate time.From a comparative study of MCM-41 and SBA-15 type materialsfunctionalized with similar organic functional groups, it has been foundthat the size of the nanopores dictates selectivity for our reactants(i.e. it appears that the steric bulk of the reactants or the channelpores of the catalysts plays a definite role in determiningselectivity). The presence of residual water in the catalysts was alsofound to affect the selectivity of the catalysts. Comparative resultswith respect to homogeneous catalysts were also presented to demonstratethe efficiency of our heterogeneous catalysts. Further, it was found outthat reaction yields for p-OH decreased when present in a reactionmixture with relatively non-polar reactants, p-Me and p-But.

Details of the syntheses of the various catalysts will now be provided.It is to be understood that certain aspects of the syntheses, such asthe specific sources of reagents, are exemplary and are not to beconstrued as limiting.

Materials and Reagents: p-Hydroxybenzaldehyde (p-OH),p-butoxybenzaldehyde (p-But), p-tolualdehyde (p-methylbenzaldehyde,p-Me), p-methoxybenzaldehyde (p-MeO), cetyltrimethylammonium bromide(CTAB), tetraethylorthosilicate (TEOS), and 3-aminoproyltrimethoxysilane(APTS), poly(ethylene oxide)-block-poly(butyleneoxide)-b/ock-poly(ethylene oxide) (P123), and nitromethane were obtainedfrom Sigma-Aldrich Corporation of St. Louis, Mo.3-mercaptopropyltrimethoxysilane (MPTS), ureidopropyltriethoxysilane(50% in methanol) (UDPS), and methyltrimethoxysilane (METS) wereobtained from Gelest, Inc. of Morrisville, Pa. Anhydrous toluene andisopropanol were purchased from Pharmco-AAPER of Brookfield, Conn. andShelbyville, Ky.

MCM-41 and SBA-15 were used as the mesoporous silica substrate material.The MCM-41 was synthesized as described previously herein. SBA-15 wassynthesized as follows: 4.0 g poly(ethylene oxide)-b/ock-poly(butyleneoxide)-block-poly(ethylene oxide) (P123), Pluronic 123, was dissolved in30 g of water and 120 g of 2 M HCl solution with stirring at about 40°C. Then 8.50 g of TEOS was added into that solution with stirring atabout 40° C. for 24 hours. The mixture was kept at 80° C. to age for 12hours under static condition. Then the solution was cooled to roomtemperature and filtered. The precipitate was washed with 1:1 ethanoland water three times (3×20 mL). The precipitate was let to dry underambient condition. The surfactant was extracted via solvent-extractionby stirring the 1 g sample in 100 mL of 1:1 volume ethanol and diethylether solution for 5 hours at about 40° C. Then it was filtered andwashed with ethanol three times (3×20 mL). Then it was allowed to dry,resulting in the SBA-15 starting material for subsequent postgrafting.

One-pot syntheses of site-isolated bifunctional mesoporous silica bygrafting were carried out as follows: Two organic groups consisting of a3-aminopropyl (AP) and a secondary organic group ureidopropyl (UDP),mercaptopropyl (MP), or methyl (ME) in about 1:1 mole ratio were graftedonto MCM-41 (or SBA-15) by stirring 1:1 mol ratio of APTS with UDPS,MPTS, or METS onto MCM-41 in isopropanol. Briefly, for example, 500 mgof the MCM-41 sample was stirred in a mixture of excess organosilanescontaining 1.842 mmol of APTS and 1.842 mmol METS in 325 mL anhydrousisopropanol under reflux at about 80° C. for 6 hours. The solution wasfiltered and the precipitate was washed with ethanol. This precipitatewas dried under ambient condition and it was labeled as APME-1.Similarly other samples were prepared; details are provided in Table 5,and FIG. 26, which depicts the general reaction scheme.

The samples obtained in one-step from the 1:1 mol mixture of the twoorganosilanes were labeled as: APUD1, APMP1, and APME1, where “AP”stands for 3-aminopropyl, “UD” for ureidopropyl, “MP” for3-mercaptopropyl, and “ME” for methyl. The subscript “1” was to indicatethe synthesis being carried out in one-step grafting. A control samplewas also prepared by grafting APTS alone (3.684 mmol) onto MCM-41 underreflux at about 80° C. in isopropanol for 6 hours. The resulting samplewas labeled as API1.

TABLE 5 Synthesis and structural data of multifunctional mesoporousmaterials and the control samples. Unit Pore Wall PoreSubstrate/Organosilanes, Cell Width Thickness BET Surface Volume, SampleSolvent (Å^(c)) (Å^(d)) (Å^(e)) Area, m²/g^(f) cm³/g MCM-41 — 45 32 13983 0.98 APUD1 MCM-41/1:1 APTS + UDPS, 44 29 15 833 0.64 IsopropanolAPMP1 MCM-41/1:1 APTS + MPTS, 43 28 15 903 0.72 Isopropanol APME1MCM-41/1:1 APTS + METS, 44 27 17 896 0.70 Isopropanol APUD2 MCM-41/APTS,45 — — — — Isopropanol; then UDPS, Isopropanol APMP2 MCM-41/APTS, 44 2717 834 0.56 Isopropanol; then MPTS, Isopropanol APME2 MCM-41/APTS, 46 2719 866 0.64 Isopropanol; then METS, Isopropanol APUD3 MCM-41/UDPS, 46 2917 928 0.69 Isopropanol; then APTS, Isopropanol APMP3 MCM-41/MPTS,Isopropanol; 44 29 15 906 0.66 then APTS, Isopropanol APME3 MCM-41/METS,46 27 19 907 0.70 Isopropanol; then APTS, Isopropanol APME4 MCM-41/1:3APTS:METS, 46 — — — — Isopropanol APME5 MCM-41/1:3 APTS:METS, 46 — — — —Toluene APME6 MCM-41/1:9 APTS:METS, 44 — — — — Isopropanol API1MCM-41/APTS, 43 28 15 950 0.65 Isopropanol API1A MCM-41/APTS, 43 27 16960 0.66 Isopropanol, 12 h UD1 MCM-41/UDPS, 44 — — — — Isopropanol SBA15— 107 61 46 557 0.75 API1- SBA-15/APTS, Isopropanol 113 — — — — SBAAPUD1- SBA-15/1:1 APTS + UDPS, 108 59 49 372 0.63 SBA Isopropanol APME1-SBA-15/1:1 APTS + METS, 109 60 49 391 0.66 SBA Isopropanol APMP1-SBA-15/1:1 APTS + MPTS, 108 60 48 353 0.60 SBA Isopropanol

Two-step synthesis of site-isolated bifunctional mesoporous silica bygrafting was carried out as follows: Two series of organoaminefunctionalized samples were synthesized with two-step sequentialgrafting of the organosilanes. The first series contained samplesgrafted with APTS followed by the secondary functional groups. 500 mgMCM-41 and 3.684 mmol of APTS were mixed with 325 mL isopropanol atabout 80° C. After stirring for 6 hours, the solution was filtered andthe precipitate was washed with ethanol. This precipitate was mixed with3.684 mmol of one of the secondary organosilanes, UDPS, MPTS, or METS,in 325 mL isopropanol and stirred at about 80° C. for 6 hours. Thesolution was filtered and the precipitates were washed with ethanol anddried under ambient conditions. The resulting samples were labeled asAPUD2, APMP2, and APME2, respectively. Similarly, by changing thesequence of grafting or by stirring the MCM-41, first in UDPS, MPTS, orMETS in isopropanol, followed by stirring the resulting samples in APTSin isopropanol, samples APUD3, APMP3, and APME3, respectively wereobtained.

Graftings of MCM-41 with APTS:METS in 1:3 and 1:9 mole ratio inisopropanol and toluene were carried out in order to prepare samplescontaining large concentrations of hydrophobic groups in the followingmanner: MCM-41 was stirred in 1:3 mol ratio of APTS:METS in isopropanoland in toluene, and in 1:9 mol ratio of APTS:METS in isopropanol atabout 80° C. for 6 hours. The solutions were filtered and theprecipitates were washed with ethanol. The precipitates were dried underambient conditions resulting in APME4, APME5, and APME6, respectively.

Grafting of organosilane onto SBA-15 in isopropanol: Additional sampleswere synthesized by stirring SBA-15 material with only APTS and in 1:1mol ratio of APTS and METS, UDPS or MPTS. Typically 500 mg of SBA-15 wasstirred in 3.684 mmol of APTS in 325 mL isopropanol under reflux atabout 80° C. for 6 hours resulting in API1-SBA-15. Stirring of 500 mg ofSBA-15 in a mixture of 1.842 mmol of APTS and 1.842 mmol METS in 325 mLisopropanol resulted in APME1-SBA. Similarly, APUD1-SBA and APMP1-SBAwere also synthesized (see Table 5).

The parent mesoporous silica and multifunctional mesoporous samples weresynthesized and studied using the chemical and physical analysistechniques described previously herein. Additional details are asfollows:

The powder X-ray diffraction was measured using a Scintag powderdiffractometer. The solid-state ¹³C (75.5 MHz) and ²⁹Si (59.6 MHz) NMRspectra were acquired on a Bruker AVANCE 300 spectrometer. For ¹³CCP-MAS NMR experiments, the applicants employed a 7.0 kHz spin rate, 5 srecycle delay, 1 ms contact time, Tr/2 pulse width of 5.2 μs, and1,000-3,000 scans using TPPM 1H decoupling. For the ²⁹Si CP-MAS NMRexperiments, we employed 7.0 kHz spin rate, 10 s recycle delay, 10 mscontact time, Tr/2 pulse width of 5.6 μs, and 256-1,024 scans using TPPM¹H decoupling. The ²⁹Si MAS NMR experiments were done with 7.0 kHz spinrate, 100 s recycle delay, π/6 pulse width of 1.9 μs, and 700-4,000scans using high power CW ¹H decoupling. The solution ¹H NMR wasmeasured by Bruker DPX-300 NMR spectrometer. The BET gas adsorptionswere measured with Micromeritics Tristar 3000 adsorption analyzer at 77K by following previously reported procedures. The TEM images were takenby using a FEI Tecnai T-12 transmission electron microscope working at120 KeV. The samples for TEM were prepared by sonicating the mesoporoussamples in ethanol for 3 minutes, casting a drop of the solution on aformvar-carbon coated copper grid and allowing it to dry under ambientconditions.

Referring in particular to Table 5, the unit cell dimensions wereobtained from the sample's d-spacing on XRD (unit cell, a_(o)=2d₁₀₀/3^(1/2) for hexagonal P_(6 mm) mesostructures). Pore width datawere obtained from the desorption branch of the N₂ gas adsorptionisotherm. Wall thickness is defines as unit cell diameter—pore diameter.BET surface areas were obtained from the N₂ adsorption isotherm with theBET method.

To briefly summarize, in this embodiment of the invention, a series ofmultifunctional mesoporous selective catalysts containing site-isolated3-aminopropyl (AP) groups, many residual silanols, and secondary organicfunctional groups, including ureidopropyl (UD), 3-mercaptopropyl (MP),or methyl (ME) groups, were synthesized. This was carried out bygrafting mixtures of the corresponding organosilanes in variousproportions in isopropanol onto the channel walls of a well-orderedmesoporous silica (MCM-41) material in one step or by sequentialgrafting of one followed by another in isopropanol and/or toluene, asshown in FIG. 26 and Table 5.

Isopropanol was chosen as a solvent for grafting because the applicantshave discovered that grafting of organosilanes in isopropanol and polar,protic solvents resulted in the most optimum site-isolated catalytic andthe most efficient solid-base mesoporous catalyst for the Henryreaction, as described previously herein. Based on this discovery, thegrafting of a mixture of two organosilanes in isopropanol under the sameprocedure was expected to yield two functional groups in the mostoptimum site-isolation. Therefore, samples APUD1, APMP1, and APME1,which were synthesized by grafting 1:1 mol ratio of the correspondingtwo organosilanes in isopropanol, were anticipated to have about a 1:1mol ratio of site-isolated AP:UD, AP:MP, and AP:ME groups, respectively.

In contrast, the grafting of one functional group in isopropanolfollowed by the second functional group in the same solvent was expectedto result in site-isolated groups in higher concentration of the first,and a relatively lower concentration of the second functional group,especially when the second grafting was done in isopropanol as comparedto being done in toluene. The applicants thought this might occurbecause the number of silanol groups available to enable a secondgrafting would be fewer after the first grafting compared to that in theoriginal parent material, and because isopropanol grafts lessorganoamine groups than toluene, as demonstrated by the applicants'previously described experiments.

Control samples, only containing site-isolated 3-aminopropyl groups,were also synthesized by stirring MCM-41 with APTS in isopropanol. Forcomparative studies of size-dependent selectivity, similarlyfunctionalized samples from SBA-15 material, whose pore diameter istwice greater than MCM-41, were also synthesized. The samplessynthesized and studied and the procedures followed to prepare thesesamples were compiled in the reaction scheme shown in FIG. 26 and inTable 5.

The original parent mesoporous silica material MCM-41 and SBA-15, andall the functionalized mesoporous materials were characterized by X-raydiffraction (XRD) (FIGS. 27A and 27B), transmission electron microscopy(TEM) (FIGS. 28 and 29), and N₂ gas adsorption (FIGS. 30A-30D). Theresults indicated that all the samples had well-ordered mesoporousstructures with unit cell dimensions of about 43-46 Å for thosesynthesized from MCM-41, and about 107-109 Å for those synthesized fromSBA-15, as shown in FIGS. 27A and 27B, respectively. The pore widthswere obtained to be between 27-29 Å for the former and 59-61 Å for thelatter. The BET surface areas ranged from 833-960 m²/g for the catalystssynthesized from MCM-41, and from 353-557 m²/g for the catalystssynthesized from SBA-15 (see Table 5). It is noted that the graftingprocedures did not affect the mesoporous structures, the pore diametersor the surface areas in any appreciable manner, as can be seen from theXRD data of FIGS. 27A and 27B, and the data in and Table 5. The presenceof well-ordered mesostructures in the samples was also corroborated byTEM images of FIGS. 28 and 29, and the Type IV isotherms obtained on theN₂ gas adsorption experiments shown in FIGS. 30A-30D. Structural datafor the samples are summarized in Table 5.

FIG. 26 is a schematic illustration of the synthetic pathways formultifunctional mesoporous samples containing various concentrations of3-aminopropyl (AP) catalytic groups, residual silanols, and a secondaryorganic group (ureidopropyl (UD), 3-mercaptopropyl (MP), or methyl (ME).The synthesis of the materials was carried out by grafting variousmixtures of organosilanes onto MCM-41 in isopropanol. The compositionsshown in the scheme were determined based on various characterizationresults.

Additionally, Table 6 is a compilation of results showing the relativecatalytic efficiency of multifunctional mesoporous catalysts synthesizedby grafting in the reaction between these p-substituted benzaldehydesand nitromethane. Referring to the column headings of Table 6, the % ofT's corresponding to organosilica silicon were obtained from ²⁹Si MASNMR. “% T” as used herein is defined as the percent of silicon atomsthat have aminopropyl or organic groups attached.

The weight percent nitrogen was obtained from elemental analysis, EA.The maximum ratio of % yield of the two reactants or the maximumselectivity was determined from the ratio of percent yield versus timeof one reactant with that of the other, from the reactions doneindividually. In the three columns to the right containing percent yieldratios of specific catalyst pairs, the yields shown for the tworeactants were taken at the time the maximum ratio of % yields occurred.

Additionally, the yield data for used in calculating the various ratiosdenoted with superscripts is as follows:

a The % yield of p-OH was >˜90% in 20 minutes.

b The yield of p-OH was ˜75% in 20 minutes.

c The yield of p-Me was ˜≧80% in 20 minutes.

d The yield of p-Me was ˜≧75% in 20 minutes.

e The yields of p-Me was less than ˜<75% in 20 minutes.

It is further noted that catalyst API1 showed a selectivity for p-OHover p-Me with a value of 1.6 times higher at 15 minutes.

TABLE 6 Relative catalytic efficiency of multifunctional mesoporouscatalysts synthesized by grafting in the reaction between p-substitutedbenzaldehydes and nitromethane. % Yield % Yield Maximum Maximum Maximump-OH:% p-Me:% % Yield Ratio of % Ratio of % Ratio of % Yield p- Yield p-of p-Me:% Yield, % p-OH/ Yield, % p- Yield, % p- But at OH at p-But atWt. % % p-But Me/% p-OH Me/% p-But Maximum Maximum Maximum Sample %T^(b) N, EA^(b) (time, min)^(c) (time, min)^(c) (time, min)^(c)Ratio^(d) Ratio^(d) Ratio^(d) MCM-41 — — — — — — — — APUD1 12 1.64 2.8(20)^(e) 1.7 (5) 3.2 (10)^(h) 93:33 27:16 27:16 APMP1 14 2.11 2.2(12)^(e) 2.4 (3) 2.4 (4)^(h) 63:29 18:8  6:2 APME1 18 2.50 1.7 (22)^(e)2.0 (3) 2.2 (5)^(h) 93:55 14:7  25:11 APUD2 — — 2.3 (10)^(e) 2.3 (5) 3.7(10)^(h) 46:20 37:16 37:16 APMP2 17 — 2.2 (18)^(e) 1.7 (4) 2.5 (4)^(h)87:40 18:13 18:11 APME2 19 — 2.5 (5)^(f) 2.0 (5) 3.8 (5) 9:4 5:3 20:5 [2.3 (20)]^(f) [60:26] APUD3 13 — 1.7 (25)^(e) 3.9 (5) 7.3 (5)^(g) 99:5876:19 76:20 APMP3 — — 1.9 (25)^(e) 3.4 (5) 5.4 (5)^(g) 99:52 72:21 72:21APME3 13 2.39 2.2 (15)^(e) 1.9 (5) 2.7 (10)^(g) 86:39 37:19 37:20 APME4— 1.57 1.8 (15)^(f) 3.2 (5) 3.7 (10) 53:29 36:11 36:11 APME5 — — 2.6(20)^(f) 2.4 (5) 3.8 (10) 73:28 61:12 28:12 APME6 — 1.46 1.8 (25)^(f)4.0 (5) 4.0 (5)^(h) 78:43 44:11 79:20 API1^(j) 15 — 2.5 (9)^(e) 1.5 (3)2.5 (4) 61:24 17:12 23:15 API1A — — 2.1 (10)^(e) 1.8 (5) 2.6 (5)^(g)67:32 40:22 40:22 API1- 17 3.15 2.0 (30) — — 68:34 — — SBA APUD1- 16 —2.1 (20) — — 50:24 — — SBA APMP1- — — 2.2 (20) — — 32:15 — — SBA APME1-— — 1.9 (30) — — 45:23 — — SBA

By using ¹³C and ²⁹Si solid-state NMR spectroscopy as shown in FIGS. 31Aand 31B, and elemental analysis, the presence and the concentrations ofthe organic groups in the catalyst samples have been analyzed. The ¹³CCP-MAS NMR spectra of the samples (FIG. 31A) showed peaks at 9.4, 24.4and 43.6 ppm. These broad peaks correspond to overlapping peaks of theα, β, γ carbons, respectively, of 3-aminopropyl (AP) group and those ofthe secondary functional groups, namely UD, or MP groups, or the peakfor ME groups depending on the secondary organosilanes grafted (FIG.31A). The chemical shifts of these functional groups are known tooverlap in solid-state NMR spectra. The peak observed at 66 ppmcorresponds to isopropoxide carbons (CH₃)₂CHO— carbons, which haveresulted from isopropanol, the solvent used for grafting. Such alkoxidepeaks often appear in ¹³C solid-state NMR spectra of functionalizedmesoporous samples synthesized by grafting, either due to reactions withsilanol groups or chemisorption.

After the organosilanes grafting, the Q3 and Q2 peaks corresponding toSiO_(1.5)(OH) and SiO(OH)₂ groups decreased while the T peakscorresponding to RSi(O)_(x)(OH)_(y) groups increased, as indicated inFIG. 31B. The “Q” peaks correspond to those silicon atoms containing noorganic or aminopropyl groups while the “T” peaks correspond to thosesilicon atoms containing organic or aminopropyl groups. From the ²⁹SiMAS NMR spectra of FIG. 31B, it was also observed that the samplesgrafted in one-step such as APMP1 and APME1 contained about 2% lessorganic groups compared to the corresponding samples grafted in twosteps such as APMP2 and APME2 (Table 6). Also the samples grafted withME groups appeared to contain about 2-3% higher organic groups than thecorresponding samples grafted with UD and MP groups under the sameconditions. These indicate that a relatively more hydrophobic andsmaller organosilane, such as METS, in a polar solvent, isopropanol, hasa higher tendency to graft onto the mesoporous silica surface than toremain in the solvent. Elemental analysis was also used to obtain theweight percent N or weight percent NH₂ groups as shown in Table 6. Thedata also exhibited that grafting of 1:1 mole ratio of APTS and UDPSresults in less grafted % N than those corresponding samples graftedwith 1:1 mole ratio of APTS and MPTS or METS. The applicants believethat due to the hydrophilic nature of the APTS and UDPS and theirtendency to form hydrogen bonding with isopropanol, they have lesstendency to go to the silanols to graft. Furthermore, the data indicatesthat grafting of 1:3 and 1:9 APTS:METS resulted in even lower % N (orless —NH₂ groups).

Comparative studies on the selective catalytic properties and efficiencyof each material for various p-substituted benzaldehydes including p-OH,p-But, p-Me, and p-MeO, either in individually or in a reaction mixturewere performed. For this latter investigation, the reaction scheme forthe selective catalysis of different p-substituted benzaldehydes withnitromethane in a mixture of two reactants by a selectivemultifunctional catalyst of the invention is as follows:

The investigation and resulting discoveries described previously hereinindicated that a bifunctional sample containing 3-aminopropyl group andmany residual surface silanols catalyzes the Henry reaction betweenp-hydroxybenzaldehyde and nitromethane effectively. While all of thesite-isolated trifunctional mesoporous catalysts described herein alsocatalyzed the Henry reaction very efficiently, their relative catalyticefficiencies varied with respect to the types and concentrations of thefunctional groups they contained and the type of the reactants used. Bytaking advantage of these differences, materials having interesting anduseful selective catalytic properties were obtained for reactants in amixture. The applicants note that that their reactions resulted inexclusively p-substituted nitrostyrene product, unlike some examples inthe literature where mixtures of nitroalcohols and nitrostyrene werereported, such as those described by Choudary et al. in J. MolecularCatal. A. 1999, 42, 361-365.

The Henry reaction was carried out by using each of theorganoamine-functionalized samples obtained above as catalysts forreactions between nitromethane and various p-substituted benzaldehydes.The reactants p-hydroxybenzaldehyde (p-OH), p-butoxybenzaldehyde(p-But), and p-methylbenzaldehyde (p-Me) were used separately and as in1:1 mol mixture of two reactants in the reaction. Typically, 21 mg ofthe functionalized mesoporous sample was added into a solution of 1 mmolp-hydroxybenzaldehyde and 10 mL of nitromethane. The reaction wasstirred at 90° C. under nitrogen and aliquots of the reaction productwere taken with a filter syringe and characterized by solution ¹H NMRover the course of the reaction. Further characterizations wereperformed by washing the catalysts to extract any possible reactants andproducts adsorbed in it. For the 1:1 mol reactant mixtures, a mixture oftwo reactants (for example, 1 mmol p-OH and 1 mmol p-But) was used andthe reaction and characterizations were carried out as above.

With regard to the solution ¹H NMR measurements, product resonancesobtained in acetone-d₆ were as follows:

p-hydroxy nitrostyrene (¹H NMR): δ 2.95 (1H, br, s), 6.97 (2H, d), 7.72(2H, d), 7.84(1H,d, J=13.5 Hz), 8.03(1H,d, J=13.5 Hz) and 9.84 (1H, s);

p-butoxy nitrostyrene (¹H NMR): δ 7.98 (1H, d, J=13.5 Hz), 7.87 (1H, d,J=13.5 Hz), 7.78 (2H, d), 7.05 (2H, d), 4.13 (2H, t), 1.82 (2H, m), 1.55(2H,m), 0.98 (3H,t); and

p-methyl nitrostyrene (¹H NMR): δ 8.07 (1H, d, J=13.5 Hz), 7.93 (1H, d,J=13.5 Hz), 7.72 (2H, d), 7.33 (1H, d), 2.45 (3H, s).

Reactant resonances obtained in acetone-d₆ were as follows:

p-hydroxybenzaldehyde (¹H NMR): δ 9.85 (1H, s), 7.81 (2H, d), 7.02 (2H,d), 2.95 (1H, br, s);

p-butoxybenzaldehyde (¹H NMR): 9.88 (1H, s), 7.86 (2H, d), 7.10 (2H, d),4.13 (2H, t), 1.82 (2H, m), 1.55 (2H, m), 0.98 (3H, t);

and

p-tolualdehyde 9.99 (¹H, s), 7.82 (2H, d), 7.42 (2H, d), 2.44 (3H, s).

Product resonances obtained in acetonitrile-d₃ were as follows:

p-hydroxy nitrostyrene (¹H NMR): δ 2.19 (1H, br, s), 6.90 (2H, d), 7.57(2H, d), 7.68 (1H, d, J=13.5 Hz), 8.00 (1H, d, J=13.5) and 9.84 (1H, s);

p-butoxy nitrostyrene (¹H NMR): δ 8.10 (1H, d, J=13.5 Hz), 7.77 (2H, d),7.71 (1H, d, J=13.5 Hz), 6.99 (2H, d), 4.06 (2H, t), 1.77 (2H, m), 1.52(2H, m), 0.96 (3H, t); and

p-methyl nitrostyrene (¹H NMR): δ 8.07 (1H, d, J=13.5 Hz), 7.93 (1H, d,J=13.5 Hz), 7.71 (2H, d), 7.32 (1H, d), 2.43(3H, s).

Reactant resonances obtained in acetonitrile-d₃ were as follows:

p-hydroxybenzaldehyde (¹H NMR): δ 9.82 (1H, s), 7.63 (2H, d), 7.05 (2H,d), 2.19 (1H, br, s);

p-butoxybenzaldehyde (¹H NMR): 9.85 (1H, s), 7.84 (2H, d), 7.05 (2H, d),4.06 (2H,t), 1.77 (2H, m), 1.52 (2H, m), 0.96 (3H, t); and

p-tolualdehyde 9.99 (¹H, s), 7.78 (2H, d), 7.39 (2H, d), 2.41 (3H, s).

FIGS. 32A-32N and FIGS. 33A-33C show the percentage yield versus timegraph of the Henry reaction of p-OH, p-But, and p-ME. These reactantswere chosen so as to allow a systematic study of the dependence ofefficiency and selectivity of reactants in the Henry reaction ondifferences in size, electronic properties, and hydrophobicity. Thecatalytic tests were carried out for each catalyst listed in Table 5 forthe reactants p-OH, p-But and p-ME individually and for differentcombinations of 1:1 mole ratio of a pair of the reactants. Comparison ofthe first series of catalysts API1, APUD1, APMP1, and APME1 (Table 6 andFIGS. 32M, 32A, 32B, and 32C, respectively), reveals high catalyticefficiency for individual reactions of p-OH and p-ME with typical yieldof about 100% in less than 30 minutes. However, the yield for p-But isslightly lower at 80% in 40 minutes. Despite this, the efficiency of thelatter is still much higher than the efficiency obtained previously byLin et al. in J. Am. Chem. Soc. 2004, 126,1010-1011, which is 50% in 24hours.

The generally low yield observed for p-But with all the catalysts wasfound to be due to electronic effects of the butoxy (BuO—) substituentacting via mesomeric deactivation of the carbonyl group and not justbecause of its steric bulk, since a control experiment performed withp-MeO showed comparative yield in 30 minutes. Further, a similar trendin the relative reactivity of p-OH, p-Me and p-But was observed forhomogeneous catalysis using 3-aminopropyltrimethoxysilane as the base innitromethane. This confirmed the slow reactivity of p-But with respectto p-OH and p-Me being due to the electronic effects. However, theapplicants believe that the differences in the efficiency among thevarious multifunctional mesoporous samples towards p-But with respect tothe other benzaldehydes may have to do with the difference in thesurface properties the catalysts and the number of catalytic sitesavailable in them. Nevertheless, it is to be understood that theapplicants' multifunctional mesoporous heterogeneous catalyst affordedmuch better yields in smaller reaction time compared to homogenouscatalyst for all the p-substituted benzaldehydes.

Furthermore, samples that contained a higher loading of organicfunctional groups generally showed lower efficiency for most of thereactants, which indicates the correlation between catalytic efficiencyand relative crowding of the catalytic sites or their site-isolation.Additionally, the catalytic efficiency of one reactant over another (orthe relative ratio of yields individually obtained for two reactants bythe same catalyst) correlates with the type of functional groups andtheir concentrations, as indicated in FIGS. 32 a-32 n and Table 6. Forinstance, referring to FIGS. 32 a, 32 d, and 32 g, the ratio of % yieldsof p-OH and p-But for individual reactions was found to be above 2.0 forsamples containing UDP and AP groups except for APUD3 (FIG. 32 g), whichshowed a ratio of % yield of 1.7, which could be attributed to the lowerconcentration of catalytic groups in this sample. Samples such as APME1,APMP3, APME4 and APME6, that contained a large concentration ofsecondary hydrophobic functional group ME and MP showed a much lowerratio of % yields for p-OH and p-But.

Furthermore, the decrease in the ratio was principally due to thedecrease in the % yield of p-OH rather than p-But over time with thelatter catalysts. Thus hydrophobic samples allowed relatively morehydrophilic p-OH limited access to the catalytic site. It is also notedthat API1 showed the highest % conversion for all the reactants comparedto other catalysts. Without wishing to be bound to any particulartheory, the applicants believe that this is most likely because itcontained the highest concentration of least crowded, most-optimumsite-isolated catalytic sites (-NH₂ groups) and a higher surface area.It is also worth noting that API1 showed much higher efficiency forhydrophobic reactants compared to 3-aminopropyl containing samplesreported by Lin et al., even if both samples have a similar number of—NH₂ groups per gram of sample.

For comparative purposes, the applicants have repeated the work of Linet al. disclosed in J. Am. Chem. Soc. 2004, 126, 1010-1011, but withdetailed reaction yield versus time plots for mixtures of p-OH, p-But,and p-Me. The applicants carried out the reaction yield versus timestudy in this case, since our experiments indicated that the selectivityin Henry reaction for a mixture of reactants was time dependent. Theapplicants have determined that the catalysts of Lin et al. lead to 100%conversion of all the reactants to products within 6 hours, as comparedto the maximum of 50% in 24 hours reported by Lin et al. Furthermore,all the catalysts of Lin et al. showed a selectivity towards the p-OHover both p-But and p-Me despite the reported selectivity of p-But overp-OH by Lin. et al. after 24 hours. Additionally, it was found thatafter the reaction was completed in 6 hours, the nitrostyrene formedstarted to convert into the Michael product as observed on the ¹H NMR,as well as possibly polymerize into poly(nitrostyrene) as observed fromthe waxy residue in the reaction flask. This thus could decrease thetrue yield of nitrostyrene and introduce error in the data, if theyields were obtained after 24 h based on the NMR peaks of reactantsversus products, as performed by Lin et al.

A comparison of the results obtained by the applicants for Lin'scatalyst and the applicants' own catalyst shows that the applicants'design of catalysts significantly improves the relative efficiency ofall the reactants in the Henry reaction by manifold, and betterselectivity is obtained for hydrophilic and hydrophobic reactants bothwhen they are reacted individually (Table 6) and in a mixture, as willbe discussed subsequently herein.

Upon comparing p-OH with p-Me, it was clearly observed that graphs ofthe % yield versus time for most of the catalysts have similar trends(FIGS. 32A-32N). In the initial reaction time, typically before 10minutes, the rate of reaction of p-Me was higher than that of p-OH inmost of the catalysts. The ratio of % yield of p-Me to p-OH during thistime (FIGS. 32 a-32 n) was consistently between 1.4 and 4.0 for all thecatalyst indicating the initial preference of the catalysts towardsp-Me. In particular, this ratio was found to be the highest in morehydrophobic samples such as APMP3, APME4, APME5, and APME6 (FIGS. 32 i,32 j, 32 k, and 32 l, respectively). After 10 minutes of reaction time,the reaction of p-Me slowed down with respect to that of p-OH and theratio of % yield of p-Me to p-OH became less than 1.0. Thus, theselectivity values of the catalysts reversed after a certain time andhence a time-dependent study was important to the determination of theexact selectivity.

It is interesting to note that this trend became more pronounced in morehydrophobic samples such as APME5 and APME6, and that homogenouscatalysis with APTS precursor in solution does not show this trend. Onthe contrary, the ratio of % yield of p-Me to p-OH was always less than1.0 in homogenous catalysis indicating that the phenomenon ofselectivity reversal is an exclusive property of the applicants'multifunctional heterogeneous mesoporous materials. Furthermore, sincethe solution NMR spectra of the reaction did not show any new productpeaks corresponding to competitive Michael reaction product,polymerization product, or any other products, the applicants' believethat this fluctuation on the graph of % yield versus time for p-Me maybe due to possible differences in the degree of adsorption anddesorption of the p-Me reactant and p-methyl nitrostyrene product in thecourse of the reaction. Furthermore, the presence of hydrogen bondingbetween the p-OH product and the silanols of the mesoporous catalystsmay also have caused this product to become trapped in the initialperiod of the reactions, making its relative yield smaller in theinitial period.

Upon comparing the catalysts' relative yield for p-OH versus p-But, theapplicants observed that all the samples showed higher yield for p-OHcompared to p-But. In particular, samples APUD1 (FIGS. 32A/32 a) andAPI1 (FIGS. 32M/32 m), which contained the most hydrophilic groups,showed the highest selectivity with values of 2.8 and 2.6, respectively,higher for p-OH than for p-But. The other catalysts also showed higherreaction rates for p-OH than for p-But with values ranging from 1.6 to2.6 times higher.

Control reactions with homogeneous catalysts were also performed. Thehomogeneous reaction was carried out by using3-aminoprpyltriethoxysilane (APTS) as the catalyst in nitromethane sincethe supported 3-aminopropyl group in the mesoporous materials is theactive catalyst. We believe that the APTS was the best controlhomogeneous catalyst. To further reduce the differences between theconditions for the homogeneous and heterogeneous catalysis, we carriedout the reaction under nitrogen to avoid any possible hydrolysis andcondensation or the triethoxysilyl groups. The homogeneous catalysisexperiment also employed similar amounts of reactants and organocatalystas in the heterogeneous catalysis.

The control reactions showed that p-OH reacted more quickly than thep-But and p-Me, and consequently, this may have contributed to thehigher rate of reaction of p-OH compared to p-But inside the mesoporouschannels. It is worth noting that the catalysts afforded over 90% yieldfor p-OH in 20 minutes of reaction time while they afforded a yield ofabout 50% for p-But in 20 minutes, as indicated in Table 7.

TABLE 7 Percent conversion in the Henry reaction of variousp-substituted benzaldehydes and nitromethane in 20 minutes reaction timeby the various trifunctional mesoporous catalysts; the reaction wasperformed at 90° C. using nitromethane as the reactant and the solvent.% Conversion % Conversion % Conversion p-OH of p- of p- Sample in 20 minBut in 20 min Me in 20 min APUD1 90 30 80 APMP1 90 45 75 APME1 90 50 80APUD2 90 45 75 APMP2 90 40 80 APME2 80 25 70 APUD3 90 40 80 APMP3 90 6090 APME3 90 50 80 APME4 75 38 70 APME5 75 25 60 APME6 75 38 80 API1 9050 70 API1A 90 50 70 (12 h - dried)

Catalysts APMP1 (FIG. 32 b) and APME1 (FIG. 32 c) showed slightlyreduced values of 2.2 and 1.7 times, respectively, of higher yields forp-OH than for p-But. This suggests that the hydrophobic groups of MP andME have reduced the preferential catalysis of p-OH over p-But. Catalystssuch as APUD2 (FIG. 32 d), APMP2 (FIG. 32 e) and APME2 (FIG. 32 f) alsoshowed similar high selectivity for p-OH over p-But with values of 2.3,2.2, and 2.5, respectively. A similar trend was also observed uponcomparing the efficiency of p-Me with p-But. Despite the substituents onthe aromatic rings of p-Me and p-But having similar hydrophobicity, thecatalytic efficiency of all the samples was consistently higher for p-Methan that for p-But and the ratio of % yields of p-Me with that of p-Butwas much higher when compared to the corresponding values obtained fromhomogeneous catalysis with APTS precursor in solution. Further, theratio of % yield for p-Me versus p-But was consistently higher than thatobserved for % yield of p-Me versus p-OH. Without wishing to be bound toa particular theory, the applicants believe that this could be due tothe steric demands imposed by the butoxy (BuO-) substituent of p-Butduring diffusion inside the pores. In other words, the bigger reactantsunderwent the reaction less slowly and gave lower yields. These resultsindicated size selectivity on the part of our functionalized catalysts.Thus our design of the catalyst allowed selectivity based on size aswell as hydrophobicity of the reactants.

To design and synthesize more hydrophobic catalysts, the applicants havegrafted the METS:APTS in 3:1 and 9:1 mole ratios in isopropanol. Thesematerials (APME4, FIGS. 32J/32 j; and APME6, FIGS. 32L/32 l,respectively) showed higher selectivity for hydrophobic group, p-Me overp-OH, with values as high as 3.2 and 4.0. The catalytic efficiency ofthese samples were slightly lower compared to samples synthesized fromAPTS only (API1) and those synthesized from 1:1 mole mixture of APTS andthe secondary organosilanes (APUD1, APMP1, and APME1) because the former(APME4 and APME6) contained less number of organoamine groups. Thelatter was confirmed by elemental analysis. Besides the AP groups, insome cases, the differences in catalytic efficiency were associated withthe second functional group. For instance, sample APUD1 (FIG. 32A/32 a)showed slightly higher efficiency than sample API1 (FIG. 32M/32 m) forp-OH reactant, with a yield of 42% versus 37% in 15 minutes, despite thefact that APUD1 contained less AP groups than API1. Furthermore, samplesAPUD2 (FIGS. 32D/32 d) and APUD3 (FIGS. 32G/32 g) consistently showed amuch higher catalytic efficiency for all the reactants. The applicantsbelieve that this is likely due to the cooperative catalytic propertiesby UD and AP groups compared to the other catalysts, as reported bySeong et al. in Angew. Chem., Int. Ed. 2005, 44, 1826-1830.

Selectivity of the catalysts for mixture of reactants indicated asimilar trend as those results obtained for reactions performed for thereactants individually. Reactions of 1:1 mol mixture of different pairof reactants were investigated with a number of catalysts. Results ofthis investigation are summarized in Table 8, and FIGS. 34A-34K, FIGS.34 a-34 k, FIGS. 35A-34E, and FIGS. 35 a-35 e. The reactions wereperformed at 90° C. using nitromethane as the reactant and the solvent.The data in each of the columns of Table 8 are based on the maximumratio of % yield of one reactant versus the other with respect to time,in a reaction mixture containing 1:1 mol ratio of both reactants.

TABLE 8 Mesoporous catalysts and control samples synthesized by graftingin various solvents and their catalytic efficiency in a reactioncontaining 1:1 mol mixtures of various p-substituted benzaldehyde withnitromethane. Maximum Maximum Maximum Selectivity SelectivitySelectivity % Yield p-Me:% % Yield p-Me:% % Yield of p- or % p-OH/ or %p-Me/ or % p-Me/ Yield p-But Yield p-OH Me:% p-But % p-But % p-OH %p-But at maximum at maximum at maximum Sample (time, min)^(b) (time,min)^(b) (time, min)^(b) selectivity^(b) selectivity^(b) selectivity^(b)APUD1 1.7 (10) — — 34:21 — — APMP1 1.8 (10) — — 36:19 — — APME1 1.9 (10)— — 21:10 — — APMP2 2.0 (15) — — 48:32 — — APME2 2.0 (10) — — 25:13 — —APME3 1.6 (15) — — 60:38 — — APMP3 2.3 (5)^(e) 1.2 (15) 3.5 (15) 12:5 56:47 35:10 APME6 1.5 (15)^(f) 2.2 (10) 3.8 (15) 36:24 36:16 48:13 API11.7 (10) 1.3 (10) 2.5 (10) 54:31 42:32 44:18

All of the catalysts showed a selectivity of about 2 for p-OH overp-But, with no significant differences among the catalysts. Thisselectivity was obtained in about 10-15 minutes of reaction time.Typical yield was found to be 70% in 10 minutes for more selectivelyreacted reactant, p-OH, with the highest being 90% and 60% at 30 minutesfor p-OH and p-But, respectively. The slight decrease in efficiency incase of 1:1 reaction is indicative of the competition between thereactants to access the catalytic sites on the basis of their stericbulk and hydrophobicity. Hydrophobic catalysts, such as APME6, showed adecreased selectivity of 1.6 for p-OH compared to p-But.

The samples grafted with 1:1 mole ratio of AP and the secondaryfunctional groups showed little selectivity for p-Me compared to p-OH,with values of about 1.0 being obtained in all cases. However, thehighly hydrophobic catalyst, APME6, showed a selectivity of 2.2 for p-Meover p-OH. Since these two reactants have similar sizes, this supportsthe premise that the catalyst does not discriminate between p-Me andp-OH on the basis of size, but instead, hydrophobicity. However,comparing p-Me with p-But, all the samples showed higher selectivity forp-Me than p-But. These values, however, varied corresponding to thehydrophobicity of the samples, with the more hydrophobic sample havingthe highest value. For instance, the values obtained were 3.8, 3.5, and2.5 for catalysts APME6, APMP3, and API1, respectively. Thus, apart fromthe intrinsic differences in the reactivity, the size selectivity of thepores results in higher reaction rate for p-Me over p-OH.

The effect of water on the materials or drying the catalysts on thecatalytic efficiency was also investigated. The results of thisinvestigation are summarized in FIG. 36 and Table 9.

TABLE 9 Effects of drying bifunctional mesoporous catalysts and itseffect on the catalytic efficiency of the materials in the Henryreaction demonstrated by catalyst API1 samples dried at different times.% Conversion of % Conversion of % Conversion of Sample p-OH in 15 minp-But in 25 min p-Me in 15 min API1 80 48 57 (1 hour drying) API1 94 6856 (3 hours drying) API1 95 66 87 (12 hours drying)

Heating of the catalyst before reactions was found to be preferable forobtaining a good yield. For example, referring to Table 9, for catalystAPI1 the optimum heating time was found to be 3 hours for p-OH and p-Butat 80° C. While further heating of the catalysts to 12 hours increasedthe yield of p-Me appreciably, it did not cause additional change on theyields of p-OH and p-But (FIG. 36). Removal of H₂O and CO₂ by heatinghas been reported to increase the strength of basic sites of solid-basecatalysts for nitroaldol condensation by Hattori in Appl. Catal. A.2001, 222, 247-259. The applicants believe that this may be the reasonfor increased catalytic efficiency of the dried samples.

In summary, we have disclosed the synthesis of selective, efficienttrifunctional mesoporous catalysts containing multiple site-isolatedfunctional groups for selective catalysis of either hydrophilic orhydrophobic reactants in the Henry reaction, as illustratedschematically in FIG. 37. This was demonstrated in the reaction betweennitromethane and various p-substituted benzaldehydes having differentsize, hydrophobicity, and electronic properties. While thesite-isolation of organoamine and silanol functional groups on thetrifunctional mesoporous materials rendered high efficiency in thereaction, the judiciously chosen secondary organic functional groupsinside the mesoporous channels have provided the materials with suitablesurface properties to allow the preferential reaction of hydrophilic orhydrophobic reactants to the other one. Further, the selective catalyticproperties for a mixture of some of the reactants were found to be timedependent. It is noted that the reaction products by these catalystswere exclusively p-substituted nitrostyrenes. By stopping the reactionat a specific time and by removing the catalyst, higher concentration ofselective reaction product from one reactant could be achieved. Thesynthetic approach employed here is simple and versatile and can beadapted to a number of other catalytic reactions and mixtures ofreactants. To the best of the applicants' knowledge, this is the firsttime that a grafting synthesis method for efficient trifunctionalmesoporous selective, efficient catalysts for both hydrophilic andhydrophobic reactants has been reported. The resulting materials shouldpotentially be useful for many reactions that are commonly employed forthe synthesis of various fine and pharmaceutical chemicals.

Optimizing Cooperative Acid-Base Bifunctional Mesoporous Catalysts forthe Henry Reaction: Effects of Site-Isolation, Concentration, andSeparation of Functional Groups

The effects of site-isolation, relative concentrations and separationdistance between bifunctional groups in acid-base bifunctionalmesoporous materials on the cooperative catalytic properties andefficiency of the materials in the base-catalyzed Henry reaction havealso been studied. The applicants have discovered that thesite-isolation and relative concentrations of the bifunctional groupscan be controlled by simple, one-step, facile grafting of organoamineson mesoporous silica at various temperatures using ethanol and tolueneas solvents; and that the separation distances between the functionalgroups can be controlled by using shorter and longer organoamines, i.e.grafting organoamines of specifically chosen lengths.

The grafting of aminororganosilanes in ethanol has resulted insite-isolated organoamine and organodiamine groups with an organoamine :silanol ratio of about 0.2 and high surface area materials. In contrast,grafting in toluene resulted in densely populated organoamines with anorganoamine : silanol ratio of about 1.0 and low surface area materials.The monoamine- and diamine-functionalized samples from ethanol affordednearly 100% yield in 15 and 30 minutes, respectively, in the Henryreaction between p-hydroxybenzaldehyde and nitromethane, while thecorresponding samples grafted in toluene gave nearly 100% yield in morethan 1 and 2.5 hours, respectively. The importance of grafting inethanol and many residual silanols to enhance the catalytic efficiencyof the materials were further confirmed by grafting additionalorganosilanes onto the bifunctional catalyst. The resulting materialsfrom ethanol exhibited only a slightly reduced catalytic efficiency,while those from toluene again showed significantly reduced efficiency.The cooperative catalytic effect by the bifunctional groups was higherfor 3-aminopropyl-functionalized samples, whose primary amines were inclose proximity with silanols, compared to3-aminoethyl(3-aminopropyl)-functionalized samples.

A comprehensive study of the effects of site-isolation, relativeconcentrations and separation distance between bifunctional groups inacid-base bifunctional mesoporous materials on the cooperative catalyticproperties and efficiency of the materials in base-catalyzed Henryreaction was performed, and is described herein. In accordance with theinvention, a series of organomonoamine- and organodiamine-functionalizedsamples with various degrees of site-isolation, relative concentrationsof the bifunctional groups, and separation distances were synthesizedvia a simple, one-step, facile grafting of organosilanes on mesoporoussilica at various temperatures using ethanol and toluene solvents. Theapplicants have performed investigations of the resulting materials'cooperative catalytic properties and efficiency in the Henry reaction.The cooperative effect by the acid and base functional groups and thesurface areas in the materials have been found to be dependent on thedegree of site-isolation, the silanol : organoamine ratio, and theseparation distance between the functional groups.

The applicants have carried out the study by preparing a series ofsamples containing various concentrations of organomonoamine,organodiamine and cyanopropyl functional groups via graftingorganosilanes onto mesoporous silica in ethanol and toluene at varioustemperatures, and by investigating the materials' catalytic propertiesin the Henry reaction. The applicants have discovered that organoamine-and organodiamine-functionalized samples from ethanol containsite-isolated organoamines and silanols and an organoamine : silanolratio of about 0.2; and that these samples provide the highestefficiency (a yield of very nearly 100% in 15 and 30 minutes,respectively) for the Henry reaction between p-hydroxybenzaldehyde andnitromethane. As noted previously, the corresponding samples grafted intoluene gave densely populated organoamines and silanols, anorganoamine:silanol ratio of about 1.0, and lower catalytic efficiency.

By further comparative studies, the applicants have discovered that thecooperative catalysis by the bifunctional groups to be distancedependent, as shorter 3-aminopropyl-functionalized samples afforded verynearly 100% yield in 15 minutes, while longer3-aminoethyl(2-aminopropyl)propydiamine-functionalized samples affordedvery nearly 100% yield in 30 minutes. The applicants believe that thislonger time to approach 100% yield is presumably due to the closerdistances between the organoamine and silanol groups in the former.Grafting of more organosilanes in ethanol onto the silanols of thebifunctional acid-base catalysts resulted in only slight reduction insilanol concentration and insignificant decrease in catalyticefficiency, while grafting of the same organosilanes in toluene resultedin large decrease in silanol concentration, poor cooperative catalysis,and significant decrease in yield. Over one hour was required toapproach 100% yield in the latter instance.

Details of the syntheses of the various catalysts in this investigationwill now be provided. As noted previously, it is to be understood thatcertain aspects of the syntheses, such as the specific sources ofreagents, are exemplary and are not to be construed as limiting.

Materials and Reagents: Nitromethane, p-hydroxybenzaldehyde,cetyltrimethylammonium bromide (CTAB), tetraethoxysilane,3-aminoproyltrimethoxysilane, 2-amino(3-aminopropyl)trimethoxysilane,and 3-cyanopropyltriethoxysilane were all obtained from Sigma-AldrichCorporation of St. Louis, Mo., and they were used as received withoutfurther purification. Anhydrous toluene and ethanol were obtained fromBDH Chemicals Ltd. of Dorset UK and were also used as received.

MCM-41 was used as the mesoporous silica substrate material, and wassynthesized as described previously herein.

FIG. 38 is an illustration summarizing reaction schemes for convertingthe mesoporous material MCM-41 into catalysts containing variousconcentrations of organomonoamine via grafting ofaminopropyltrimethoxysilane onto MCM-41 in ethanol and toluene atvarious temperatures. Details of the various syntheses are as follows:

Synthesis of Monoamine-Functionalized Mesoporous Silica in Ethanol: Amonoamine functionalized mesoporous material was synthesized by grafting3-aminpropyltrimethoxysilane (APTS) onto MCM-41. Briefly, 500 mg of theMCM-41 sample was stirred in excess amount, 0.27 g (1.51 mmol), of APTMSand 200 mL anhydrous ethanol under reflux at about 78° C. for 6 hours.The solution was filtered and the precipitate was washed withdichloromethane, then with ethanol. The precipitate was allowed to dryunder ambient conditions and it was labeled as AP-E1.

Synthesis of Monoamine-Functionalized Mesoporous Silica in Toluene: Twoorganoamine samples were prepared by grafting3-aminpropyltrimethoxysilane (APTS) onto MCM-41 in toluene. Briefly, 500mg of the MCM-41 sample was stirred in excess amount, 0.66 g (3.68mmol), of APTS and 200 mL toluene at about 78° C. The solution wasfiltered and the precipitate was washed with dichloromethane, and thenwith ethanol. The precipitate was allowed to dry under ambientconditions and it was referred to as AP-T1. A second sample was preparedin the same manner, but under reflux at about 112° C. for 6 hours. Thissample was referred to as AP-T2.

Grafting of More Organosilane onto AP-E1 in Ethanol and Toluene: Furthergrafting of two different organosilanes on sample AP-E1 in ethanol andtoluene was carried out. Typically, 300 mg of the AP-E1 prepared abovewas placed in a small flask and was stirred in an excess amount, 0.40 g(2.23 mmol) of 3-aminopropyltrimethoxysilane (APTS) under reflux atabout 78° C. for 6 hours in 200 mL ethanol. The solution was filteredand the precipitate was washed with dichloromethane and ethanol. Theprecipitate was allowed to dry under ambient conditions and it was namedAP-EE1. A second sample was prepared with the same procedure, but in 200mL of toluene at about 78° C., and this sample was named AP-ET1.

Similarly, 3-cyanopropyltriethoxysilane (CPTS) was grafted on sampleAP-E1 in ethanol and toluene. Typically, 300 mg of sample AP-E1 wasstirred in an excess amount, 0.40 g (2.23 mmol), of CPTS under reflux atabout 78° C. for 6 hours in ethanol. The solution was filtered and theprecipitate was washed with dichloromethane and ethanol and it wasallowed to dry under ambient conditions. The resulting precipitate wasdenoted as AP-EE2. A second sample was prepared in the same way, but intoluene at about 78° C. and this sample was denoted as AP-ET2.

Control Samples (Treatment of AP-E1 in Ethanol and Toluene): To preparecontrol samples, AP-E1 was stirred in ethanol and toluene withoutorganosilanes. Typically, 300 mg of sample AP-E1 was stirred underreflux at about 78° C. for 3 hours in ethanol. The solution was filteredand the precipitate was washed with dichloromethane and ethanol andallowed to dry under ambient conditions. The resulting precipitate wasdenoted as AP-E1A. A second sample was prepared the same way, but intoluene at about 78° C., and the resulting sample was named AP-E1B.

Additional reactions were also performed to convert the mesoporousmaterial into a series of organodiamine-functionalized catalystscontaining various concentrations of organodiamine via grafting ontoMCM-41 in ethanol and toluene at various temperatures. Details of thesesyntheses are as follows:

Synthesis of Diamine-Functionalized Mesoporous Silica by Grafting inEthanol and Toluene: Two mesoporous samples functionalized withorganodiamine groups were prepared by grafting[3-(2-aminoethylamino)propyl]trimethoxysilane (AAPTS) in ethanol andtoluene. Briefly, 500 mg of the MCM-41 sample was stirred in excessamount, 0.50 g (2.23 mmol), of AAPTS and 200 mL ethanol under reflux atabout 78° C. for 6 hours. The solution was filtered and the precipitatewas filtered with dichloromethane, and then with ethanol. Theprecipitate was allowed to dry under ambient conditions and it wasdenoted as AAP-E1.

Similarly, grafting of excess amount, 0.50 g (2.23 mmol), of AAPTS onMCM-41 in 200 mL toluene under reflux at about 112° C. for 6 hours wascarried out. The solution was filtered and the precipitate was washedthe same way as above. The resulting sample was referred to as AAP-T1.

The parent mesoporous silica and the series of organomonoamine- andorganodiamine-functionalized samples were synthesized and studied usingthe chemical and physical analysis techniques described previouslyherein, or techniques/instruments similar thereto. Additional detailsare as follows:

The powder X-ray diffraction was measured using a Scintag powderdiffractometer. Small angle X-ray scattering was measured withSynchrotron radiation at the Cornell High Energy Synchrotron Source(CHESS) as well as by using a Bruker-Axs Nanostar System. Thesolid-state ¹³C (75.5 MHz) and ²⁹Si (59.6 MHz) NMR spectra were acquiredon a Bruker AVANCE 300 spectrometer. For ¹³C CP-MAS NMR experiments, theapplicants employed 7.0 kHz spin rate, 5 s recycle delay, 1 ms contacttime, Tr/2 pulse width of 5.2 μs, and 1000-3000 scans using TPPM 1Hdecoupling. For the ²⁹Si CP-MAS NMR experiments, we employed 7.0 kHzspin rate, 10 s recycle delay, 10 ms contact time, Tr/2 pulse width of5.6 μs, and 256-1024 scans using TPPM ¹H decoupling. The ²⁹Si MAS NMRExperiments were done with 7.0 kHz spin rate, 100 s recycle delay, Tr/6pulse width of 1.9 μs, and 700-4000 scans using high power CW ¹Hdecoupling. The thermogravimetric analysis was carried out with a Q-500Quantachrome Analyzer (TA-Instruments). The GC-MS was measured withHP-5971 GC-MS spectrometer. The solution ¹H NMR was measured by BrukerDPX-300 NMR spectrometer. The BET gas adsorptions were measured withMicromeritics ASAP 2020 volumetric adsorption analyzer at 77 K byfollowing previously reported procedure. The TEM images were obtainedwith a JEOL 1200 EX TEM instrument.

The above syntheses are summarized as follows. A series of monoamine-and diamine-functionalized mesoporous acid-base bifunctionalizedmaterials with various concentrations of organoamine and silanol groupswere synthesized by grafting 3-aminopropyltrimethoxysilane (APTS),2-aminoethyl(3-aminopropyl)trimeth-oxysilane (AAPTS) and3-cyanopropyltriethoxysilane (CPTS) onto mesoporous silica (MCM-41)using ethanol as a solvent, as shown in FIG. 38 and Table 10. Referringto Table 10, the unit cell data were obtained from the sample'sd-spacing on XRD (unit cell, a_(o)=2 d₁₀₀/3^(1/2) for hexagonal P_(6 mm)mesostructures). The BJH pore diameters were obtained from theadsorption branch on the N₂ gas adsorption isotherm. Wall thickness isdefined as Unit Cell Diameter—Pore Diameter.

TABLE 10 Synthesis and structural and composition data for monoamine-and diamine-functionalized mesoporous materials and other controlsamples prepared by grafting organosilanes onto MCM-41 in ethanol andtoluene. BJH Pore Wall Substrate + Organosilane, Solvent Unit Cell BETSurface Diameter Thickness Sample (Grafting Temperature)^(b) (Å)^(c)Area (m²/g)^(d) (Å)^(d) (Å)^(f) MCM-41 — 44.3 1030^(e) 34.1^(e) 10.2^(e)AP-E1 MCM-41 + APTS, Ethanol (78° C.) 44.4  906^(e) 31.4^(e) 13.0^(e)AP-T1 MCM-41 + APTS, Toluene (78° C.) 45.6  259^(e) 31.5^(e) 14.1^(e)AP-T2 MCM-41 + APTS, Toluene (112° C.) 44.4  60^(e) 30.6^(e) 13.8^(e)AP-EE1 AP-E1 + APTS, Ethanol (78° C.) 44.2  990 29.4 14.8 AP-ET1 AP-E1 +APTS, Toluene (78° C.) 44.0  73 21^(g) AP-EE2 AP-E1 + CPTS, Ethanol (78°C.) 44.5 1100 30.0 14.5 AP-ET2 AP-E1 + CPTS, Toluene (78° C.) 44.1  87228.5 15.6 AP-E1A AP-E1 + Ethanol (78° C.) 44.0 1202 29.3 14.7 AP-E1BAP-E1 + Toluene (78° C.) 43.8 1888 29.6 14.2 AAP-E1 AAPTS, Ethanol (78°C.) 44.2 1021 32.3 9.8 AAP-T1 AAPTS, Toluene (112° C.) 43.6  85 29.014.6

The MCM-41 material was synthesized as reported previously herein. Thesurfactant template was extracted by stirring the as-synthesized MCM-41in a dilute acid/methanol solution to leave more surface silanol groups.The grafting of site-isolated organoamine groups onto the surfacesilanols of the materials was carried out by stirring APTS and AAPTS inethanol at 78° C., which resulted in samples AP-E1 and AAP-E1,respectively. The grafting of densely populated organomonoamine wereobtained by grafting APTS on MCM-41 in toluene at 78° C. and in refluxat 112° C. to provide samples AP-T1 and AP-T2, respectively. Similarly,densely populated organodiamine were formed by grafting of AAPTS intoluene on MCM-41 at 78° C. to result in sample AAP-T1. Furthermore,control samples were prepared by grafting more APTS onto AP-E1 usingethanol and toluene to afford samples AP-EE1 and AP-ET1, respectively.Similarly, 3-cyanopropyltriethoxysilane (CPTMS) was grafted onto AP-E1in ethanol and toluene to result in AP-EE2 and AP-ET2, respectively.Additional control samples were obtained by stirring AP-E1 in ethanoland toluene without organosilanes to result in AP-E1A and AP-E1 B,respectively.

The structures of the pre-made mesoporous sample (MCM-41) and theresulting organoamine-functionalized mesoporous samples werecharacterized by powder X-ray diffraction (XRD) and small angle X-rayscattering (SAXS). FIG. 39A depicts the powder X-ray diffractionpatterns of MCM-41 compared with the following organomonoaminefunctionalized mesoporous samples prepared by grafting in ethanol andtoluene: AP-E1, AP-T1, AP-T2, AP-EE1, AP-ET1, AP-EE2, and AP-ET2. FIG.39B depicts the powder X-ray diffraction patterns of MCM-41 comparedwith organodiamine functionalized samples AAP-E1 and AAP-T1.

Referring first to FIG. 39A, the XRD patterns of the MCM-41 and all theorganoamine grafted samples showed a sharp (100) Bragg reflection and atleast two additional peaks corresponding to (110) and (200) Braggreflections, which indicated that all the samples have highly orderedhexagonal, P_(6 mm), mesostructures. From the d-spacing on XRD, the unitcell dimensions of the materials were calculated to be about 43.8-45.6 Å(Table 10). As can also be seen in FIG. 39A, only a minor reduction inthe intensities of their Bragg reflections was observed in theorganoamine-functionalized samples compared to MCM-41, which indicatedthat the grafting of organosilanes onto the MCM-41, both in ethanol andtoluene, did not cause major changes in the mesostructures.

Without wishing to be bound to any particular theory, the applicantsbelieve that the slight decrease in the Bragg reflections in samplesgrafted in toluene, such as in AP-T1 and AP-T2, compared to samplesgrafted in ethanol, such as in AP-E1 and AP-EE1, were possibly due tothe slight reduction in electron contrast caused by the grafting of moreorganoamine groups in the former than in the latter. The slightnoticeable reduction in unit cell dimension of AP-T2 compared to AP-T1and AP-E1 was probably due to the slight shrinkage of the mesostructurescaused by the condensation of residual surface silanols in the materialsat higher temperatures, under which AP-T2 was prepared. The well-orderedmesostructures in these materials were also further confirmed by smallangle X-ray scattering (SAXS) measurements (see FIGS. 39C and 39D),which exhibited four or more Bragg reflections.

FIG. 40(A)-(F) are transmission electron microscopy images of (A) MCM-41mesoporous silicate starting material, and selected organomonoamine andorganodiamine mesoporous catalysts synthesized therefrom, (B) AP-E1, (C)AP-T1 (D) AP-T2, (E) AAP-E1 and (F) a high resolution TEM image ofAP-E1, respectively. The structures of the materials were furtherconfirmed by these TEM images, which showed nanorod shaped particleshaving mesoporous structures. Supramolecular synthesis in basic solutionfrom pure tetraalkoxysilanes has been reported by Huh et al. in Chem.Mater. 2003, 15, 4247-4256 to form such nanorod shaped mesoporousparticles while the presence of a few mmol of organosilanes leads tospherical mesoporous particles.

FIG. 41A depicts nitrogen gas adsorption isotherms of MCM-41 comparedwith those for organomonoamine mesoporous catalysts AP-E1, AP-T1, andAP-T2; and FIG. 41B depicts nitrogen gas adsorption isotherms of MCM-41compared with those for organodiamine mesoporous catalysts AAP-E1 andAAP-T1. FIGS. 41C-4J are the individual isotherms and pore-sizedistribution data for the AAP-E1, AAP-T1, AP-EE1, AP-ET1, AP-EE2,AP-ET2, AP-E1A, and AP-E1B materials; and FIGS. 5B-5E are the individualisotherms and pore-size distribution data for the MCM-41, AP-E1, AP-T1,and AP-T2 materials. These N₂ gas adsorption measurements of the samplesshowed Type IV isotherms with no significant hysteresis for all of thesamples, which was characteristic of the presence of well-orderedmesoporous structures in the materials. The BET surface areas of thesamples, however, varied very significantly depending on the synthesisconditions employed. The surface areas of MCM-41, AP-E1, AP-T1, andAP-T2 were 1030, 906, 260, and 60 m²/g, respectively, while the surfaceareas of AAP-E1 and AAP-T1 were 905 and 80 m²/g, respectively. Since allof the materials showed ordered mesoporous structures, the applicantsbelieve that the decrease in surface area of the organoamine-graftedsamples compared to MCM-41 was likely caused exclusively by the densityof the organoamines in the mesopores.

Similar trends in lower surface areas were also observed for the controlsamples AP-EE1, AP-ET1, AP-EE2 and AP-ET2 (see Table 10). The samplesgrafted in toluene and at higher temperatures showed significantdecrease in surface areas compared to samples grafted in ethanol. Thisindicates that grafting in toluene and at higher temperatures favoredimmobilization of higher concentration of organoamine groups in thematerials. While the BJH pore size distribution of the samples exhibiteda monodisperse pore size distribution, the pore diameters decreased moresignificantly for samples containing more organoamines and organicgroups, particularly those grafted in toluene. For instance, the porediameter of the MCM-41 was 34.1 Å while the pore diameters of AP-E1,AP-T1, and AP-T2 were 31.4, 31.6, and 30.6 Å, respectively. Similarly,the pore diameters of the AAP-E1 and AAP-T1 were 34.4, and 29.0 Å,respectively. Similarly, the wall thickness was higher for samplesgrafted in toluene than samples grafted in ethanol. It is also worthnoting that the pore volume reduction was higher in samples grafted intoluene than in ethanol.

The presence and concentrations of the organic functional groups in thematerials after grafting were characterized by combinations ofsolid-state NMR spectroscopy and thermogravimetric analysis. FIG. 42Adepicts ¹³C CP-MAS solid-state NMR spectra of MCM-41, AP-E1, AP-T1,AP-T2, AAP-E1, AAP-T1; and FIG. 42B depicts ²⁹Si MAS and CP MASsolid-state NMR spectroscopy of MCM-41, AP-E1, AP-T1, AP-T2, AAP-E1,AAP-T1, and AP-EE2. FIG. 42C depicts a comparison of the ²⁹Si CP MAScompared with ²⁹Si MAS NMR spectra for the monoamine and diaminefunctionalized mesoporous samples. The ¹³C CP-MAS NMR of FIG. 42Aconfirmed the presence of 3-aminopropyl, 2-aminoethyl(3-aminopropyl),and 3-cyanopropyl groups in APTS, AAPTS, and CPTS-functionalizedsamples. The intensity of the peaks corresponding to these functionalgroups was higher in samples grafted in toluene than correspondingsamples grafted in ethanol, indicating the grafting of more organicgroups in toluene than in ethanol.

These were further confirmed by ²⁹Si MAS and ²⁹Si CP-MAS NMR spectra ofFIG. 42B. The ²⁹Si MAS NMR spectra indicated that the APTS and AAPTSfunctionalized samples grafted in toluene, AP-T1, AP-T2 and AAP-T1,showed more T peaks corresponding to Si(Organic)(O)_(x)(OH)_(1.5-x)silicon atoms than the corresponding samples grafted in ethanol, AP-E1and AAP-E1. In fact, the T peaks on ²⁹Si MAS NMR for AP-E1 and AAP-E1samples were barely observable. However, these peaks were clearlyobservable on ²⁹Si{¹H} CP-MAS NMR spectra. The results indicated thatthe samples grafted in ethanol resulted in very few organoamines butmany residual silanols compared to the corresponding samples grafted intoluene. From the relative peaks on the ²⁹Si MAS NMR spectra, therelative composition of the 3-aminopropyl groups and silanol groups ineach material was determined. These compositions are summarized in Table11.

TABLE 11 Data of concentrations of organoamine and silanol groups inorganoamine-functionalized samples obtained from solid-state NMR and TGAresults. mmol mmol [Si—OH]/[Si—R—NH₂] Wt. % of Wt. % change Si—R—NH₂/gSi—OH/g (or Organoamine from between Sample sample sample[Si—R—NH₂]/[Si—OH]) ²⁹Si MAS NMR 100-600° C. AP-E1 1.32 6.8 5.1 (0.2)7.8 10.7 AP-T1 4.2 3.8 0.9 (1.1) 15.5 14.8 AP-T2 4.3 3.0 0.7 (1.4) 25.016.8 AAP-E1 1.5 9.4 6.2 (0.2) 15.4 12.4 AAP-T1 2.4 4.1 1.7 (0.6) 24.021.5

With regard to the data in Table 11, the mmol of Si—R—NH₂ per unit gramof organoamine-functionalized sample was obtained by integrating the Tpeaks on ²⁹Si MAS NMR, i.e. [Si—R—NH₂]=T3+T2+T1. The mmol of Si—OH inunit gram of organoamine-functionalized sample was obtained byintegrating the T and Q peaks on ²⁹Si MAS NMR, i.e. total[Si—OH]=Q3+2(Q2)+3(Q1)+T2+2(T1). The ratio of the number of Si—OH andSi-organoamine ([Si—OH]/[Si—R—NH₂]) group was calculated by obtainingthe total number of [Si—OH]=[silanols]=Q3+2(Q2)+3(Q1)+T2+2(T1) and thetotal number of organoamine groups=[Si—R—NH₂]=T3+T2+T1. The weightpercent of organoamine was obtained by integrating the T peaks(T1+T2+T3) on ²⁹Si MAS NMR. The weight percent change was obtained fromTGA in the range of 100-600° C.

In studying these NMR data, the applicants have discovered aninteresting relationship between the percent of silanol and organoaminegroups as summarized in Table 11. By integrating the Q and T peaks, thetotal number of silanol groups per unit mass of material was obtainedfrom Q3+2(Q2)+3(Q1)+T2+2(T1), while the overall numbers of Si—R—NH₂groups per unit mass of material was obtained from T3+T2+T1. Similarly,the weight percent of the organoamine groups and mmol NH₂ catalyticsites per unit mass of sample were calculated.

Thermogravimetric analysis was further used to confirm the solid-stateNMR results. FIG. 43A shows the thermogravimetric analyses of the MCM-41sample compared with the monoamine and diamine functionalized samplesgrafted in ethanol and toluene: AP-E1, AP-T1, AP-T2, AAP-E1, and AAP-T1.These TGA traces showed a weight loss below 100° C. by all the samples,which was due to evaporation of physisorbed water from the samples. Mostimportantly, the TGA traces showed a weight reduction in the range of100-600° C., which is mainly due to the loss of organoamine groups aswell as due to some loss of chemisorbed water and water of condensationof the silanols. The latter two were confirmed from the TGA trace of thepure MCM-41, which has no organoamine group and which showed a weightloss of about 7% in the range of 100-600° C. Despite the 7% weight lossdue to condensation of silanols in the range of 100-600° C. for MCM-41,the weight loss in the corresponding organofunctionalized samples wouldbe significantly less than that for MCM-41, as the latter contained lessnumber of surface silanols.

Analysis of the TGA traces in the range of 100-600° C. exhibited sampleAP-E1 to have a weight loss of 10.7% while AP-T1 and AP-T2 to haveweight losses of 14.6 and 16.6%, respectively. Similarly, AAP-E1 showedweight loss of 12.4% while AAP-T1 showed a weight loss of 21.5% asindicated in Table 11. From these results, it was again clear that themesoporous samples grafted in ethanol to have significantly less numberof organoamines than corresponding samples grafted in toluene and athigher temperatures. Further analysis revealed AP-T2 to have 2.0% moreweight loss in the range of 100-600° C. than AP-T1, and AP-T1 in turn tohave 4% more weight loss than AP-E1. This indicates that the graftingdensity depends more on the type of the solvent used than the graftingtemperature. Further comparative TGA analysis indicated AP-E1 and AP-T1to have ˜1.7 and 6.7% less weight losses than AAP-E1 and AAP-T1 in therange of 100-600° C. This was clearly mainly due to the lower molecularweight of the organoamine compared to organodiamine (or by theadditional aminoethylene group, —NHCH₂CH₂—, in the organodiamines), asthe mmol Si—R—NH₂ in the two materials were similar.

The applicants note that such comparative studies of weight losses dueto organoamine groups in these samples based on TGA traces requirescareful analysis because the weight loss in the range of 100-600° C. isnot only caused by the loss of organoamine groups but also by loss ofwater from condensation of silanols. Additionally, the relative numbersthese two groups in the materials are inversely related. For instance,based on solid-state NMR results, samples AP-T1 and AP-T2 have largernumbers of organoamine groups but fewer number of silanol groupscompared to sample AP-E1. Consequently, the percentage of weight lossdue to condensation of silanol groups in AP-T1 and AP-T2 in the range of100-600° C. should be smaller than that in AP-E1. This implies that theactual difference in percentage of weight losses due to the organoaminegroups between AP-E1 and AP-T1 as well as AAP-E1 and AAP-T1 should, infact, be higher than what was obtained from the TGA analysis and couldparallel those obtained from the solid-state NMR analysis. For instance,the weight loss by sample AP-T1 from the TGA traces in the range of100-600° C. was 4.1% higher than that for AP-E1 without taking silanolsinto account while the value obtained from solid-state NMR was 7.7%higher, as shown in Table 11. From combinations of the NMR and TGAresults, the mmol of silanols Si—R—NH₂ catalytic sites in the sampleswere determined, and possible compositions of the materials werecompiled in the reaction scheme shown in FIG. 38.

Previously in this specification, the applicants disclosed mesoporoussamples with site-isolated 3-aminopropyl groups that are much moreefficient catalysts in base-catalyzed reactions than correspondingsamples with densely populated 3-aminopropyl groups due to the highersurface area and the cooperative effects of bifunctional groups in theformer. In this section of the specification, we now reportcomprehensive effects of site isolations, concentrations and separationdistances between organomonoamine (organodiamine) and silanolbifunctional groups on the cooperative catalytic properties andefficiency of the materials in base-catalyzed reactions.

The applicants performed the Henry reaction betweenp-hydroxybenzaldehyde and nitromethane by using all theorganoamine-functionalized catalyst samples of the invention prepared asdescribed herein and listed in Table 12 as catalysts. The reactionscheme was as follows:

Typically, 20 mg of the aminofunctionalized mesoporous sample was addedinto a solution of 122 mg (1 mmol) p-hydroxybenzaldehyde and 10 mL ofnitromethane. The reaction was stirred at 90° C. (or at 50° C.) undernitrogen and aliquots of the reaction product were taken with a filtersyringe and characterized by solution ¹H NMR and GC-MS over the courseof the reactions. The percent yield and conversion were determined byusing ¹H NMR (Bruker DPX-300 MHz) spectra. Resonances in acetone-d₆wereas follows:

p-hydroxy nitrostyrene (¹H NMR): δ 2.85 (1H, br, s), 6.96 (2H, d), 7.71(2H, d), 7.83 (1H, d, J=13.5 Hz), and 8.04 (1H, d, J=13.5 Hz); and

p-hydroxybenzaldehyde (¹H NMR): δ 2.95 (1H, br, s), 7.05 (2H, d), 7.8(2H, d), and 9.84 (1H, s).

FIG. 44A depicts the catalysis time plots of AP-E1, AP-T1, AP-T2,AAP-E1, AAP-T1 and control sample MCM-41; and FIG. 44B depicts thecatalysis time plots of sample AP-E1 compared with AP-EE1, AP-ET1,AP-EE2, and AP-ET2. Table 12 summarizes the applicants' mesoporouscatalysts and control samples synthesized by grafting in varioussolvents and their catalytic efficiency in a reaction betweenp-hydroxybenzaldehyde and nitromethane. With regard to the data in Table12, the Henry reaction was performed at 90° C. using nitromethane as thereactant and the solvent unless mentioned otherwise. The mmol NH₂/gsample data were obtained from ²⁹Si MAS NMR. TON is defined as theturnover number, i.e. mmol product/mmol catalyst. For samples AAP-E1 andAAP-T1, the reaction was done at 50° C. in nitromethane. For sampleAP-E1, the reaction was performed at 90° C. using toluene as a solventin the presence of a stoichiometric amount of nitromethane.

The yields of the reaction were monitored over a course of reaction timeby solution ¹H NMR and GC-MS. For comparison purposes, the same amountof catalysts and reagents were used in the reactions. As can be seen inFIGS. 44A and 44B, both the monoamine- and diamine-functionalizedsamples synthesized in ethanol, AP-E1 and AAP-E1, were much moreefficient than the corresponding samples grafted in toluene, AP-T1,AP-T2, and AP-T3, despite the former samples having about four timeslower numbers of organoamine groups than the latter. The AP-E1 andAAP-E1 gave very nearly 100% yield in 15 and 30 minutes; correspondingturn-over-numbers (TON) of 37.5 and 7.6; and turn-over-frequencies of150.0/h and 30.4/h, respectively. To the best of the applicants'knowledge, these values indicate these materials to be the mostefficient catalysts of all mesoporous materials reported for Henryreactions in the literature to date.

TABLE 12 Mesoporous catalysts and control samples synthesized bygrafting in various solvents and their catalytic efficiency in areaction between p- hydroxybenzaldehyde and nitromethane. mmol NH₂/gYield (%) Yields (%) in TON in TOF in 15 min Sample sample [Si—OH]/[—R]in 15 min various times 15 min (TON/h) MCM- — 6.4 0 0 — — 41 AP-E1 1.35.1 99.0 100 (16 min) 37.5 150.0 AP-T1 4.2 0.9 52.5 95.5 (39 min) 6.224.8 AP-T2 4.3 0.7 3.1 11.7 (1 h) 0.6 2.4 AAP-E1 1.5 6.2 64.5 100 (30min) 7.6 30.4 AAP-T1 2.4 1.7 10.6 29.9 (1 h) 2.3 9.2 AP-EE1 — — 90.590.5 (15 min) — — AP-ET1 — — 82.0 98 (30 min) — — AP-EE2 — — 58.8 68.7(19 min) — — AP-ET2 — — 26.8 98.4 (2 h) — — AP-E1A — — 82.0 93 (20 min)— — AP-E1B — — 96.2 100 (20 min) — — AAP-E1 — — 81.0 100 (30 min) — —AAP- — — 9.7 61 (1 h) — — E1^(e) AAP- — — 9.2 45 (1 h) — — T1^(e)AP-E1^(f) — — 98 100 (18 min) — —

For comparison, the control samples that the applicants prepared bygrafting aminorganosilanes in toluene at 78° C., AP-T1 and AAP-T1, gavea 12.0% and 29.9% yield in about 1 hour, while in contrast, catalystreported by Demicheli et al. in Tetrahedron Lett. 2001, 42, 2401-2403using toluene gave 96% in 1 hour. The applicants believe that thedifferences in efficiency between these five catalysts can be explainedby the differences in site-isolation, the organoamine:silanol ratio, andthe surface areas of the materials. For instance, samples AP-E1 andAAP-E1 contained higher surface areas and more silanol groups thansamples AP-T1, AP-T2, and AAP-T1, and consequently, the former resultedin better cooperative and efficient catalysis. The presence of largenumber of residual silanols, the formation of site-isolated organoaminesand silanol groups and the higher surface areas in AP-E1 and AAP-E1materials would be responsible for the increased cooperative catalyticefficiency in these samples. Related mechanisms and differences ofcooperative catalysis by the amines and silanol groups in AP-E1, AP-T1,and AAP-E1 samples in the selected Henry reaction are shown in FIG. 45.The silanol:organoamine ratio obtained from solid-state NMR for eachmaterial is also shown therein.

The applicants believe that the higher efficiency of sample AP-E1compared to sample AAP-E1 is also noteworthy. The concentration ofprimary amines (—NH₂ groups) in AP-E1 and AAP-E1 was 1.3 and 1.5 mmol/g,respectively, which were similar, while their respective silanols were6.8 and 9.4 mmol/g. These would give a [Si—OH]:[Si-Organoamine] ratio of5:1 and 6:1 in AP-E1 and AAP-E1 samples, respectively. The surface areasof AP-E1 and AAP-E1 were 906 and 889 m²/g, respectively, which were alsocomparable. Based on these results and considering the presence ofadditional 1.5 mmol/g secondary amine groups in the diaminefunctionalized sample, AAP-E1, one would expect AAP-E1 to be a moreefficient catalyst. However, AP-E1 unexpectedly showed a highercatalytic efficiency or turn-over-number (37.5) than AAP-E1, whichshowed a turn-over-number of 7.6.

This indicates the importance of the shorter distance between theprimary amine and the surface silanol groups in the AP-E1, which allowedbetter cooperative effects by the amine group and the silanols, ascompared to that in AAP-E1, whose primary amine is farther from thesurface silanols (FIG. 45). Despite that the secondary amine groups inAAP-E1 are close to silanols, they were much less efficient catalystsfor the Henry reaction compared to primary amines, as reported byShimizu et al. in Tetrahedron Lett. 2002, 43, 9073-9075. In the proposedcooperative catalytic mechanism shown in FIG. 45, a nitromethyl anionwould remain close to the primary amine group, which becomes ammoniumion. The nitromethyl anion can attack the silanol-activated carbonylcarbon of benzaldehyde more easily if the amine and silanols are closeto each other as in AP-E1 compared to in AAP-E1. A similar ion-paircatalytic mechanism was also proposed recently by Katz et al. in J. Am.Chem. Soc. 2006, 128, 3737-3747.

Further analysis of the relationships between the ratio of[Si—OH]:[Si—R] and the efficiency of the catalysts also revealed anotherinteresting discovery. From the data in Table 12, it was clear thatsample AP-E1 with a [Si—OH]:[Si—Pr—NH₂] ratio of 5:1 gave more efficientcatalysis compared to samples AP-T1 and AP-T2 whose [Si—OH]:[Si—Pr—NH₂]was 1:1. Similarly, AAP-E1 with [Si—OH]:[Si—Pr—NH₂] of 6:1 is a muchbetter catalyst than AAP-T1, which has a [Si—OH]/[Si—Pr—NH₂] of about2:1. These results indicated that a significantly higher number ofsilanols with respect to organoamine groups would be needed to result ineffective cooperative catalysis and to leave the materials with highersurface areas. From the applicants' studies, the materials with a[Si—OH]:[Si—Pr—NH₂] ratio close to ˜5:1, which consists of 5 silanolsfor every organoamine group, have resulted in the highest efficiencyknown to us. Interestingly, a [Si—OH]:[Si—Pr—NH₂] ratio of 1:1, as inAP-T2, does not give an ideal cooperative effect. The applicants believethat this is possibly due to the lower surface area as well as thesteric hindrance caused by the densely populated, longer organoaminesaround surface silanols in AP-T2, which inhibit the activation ofbenzaldehyde carbonyl groups by silanols for the Henry reaction.

The cooperative effects by the organoamine and silanol groups and theincreased catalytic efficiency occurred better in samples grafted inethanol. These samples contained less organoamines, more silanols andhigh surface areas. On the other hand, more densely populatedorganoamine, less silanols and less surface areas occurred when thegrafting was done in toluene. In ethanol, which is a polar solvent, theaminorganosilanes form hydrogen bonding with the solvent. This reducestheir grafting tendency onto the surface silanol groups of themesoporous materials, whereas in non-polar solvents such as toluene, thehydrophilic aminorganosilanes have a strong tendency to go to and graftonto the hydrophilic mesoporous silica surfaces. The various dielectricconstants used in the analysis are provided in Table 13.

TABLE 13 Dielectric constants and boiling points of the solvents used invarious catalyst syntheses. Chemical Dielectric Boiling Solvent formulaconstant point Ethanol CH₃CH₂OH 24  78° C. Toluene C₆H₅CH₃ 2.4 111° C.

Moreover, aminorganosilanes tend to aggregate through hydrogen bondingin toluene and result in densely populated, aggregated organoamines. Theformation of organoamine clustering and grafting of organoamines asaggregates on the surface inhibit cooperative effects by organoaminesand silanols. Furthermore, a significant reverse reaction betweengrafted organoamine groups and ethanol could take place in ethanol,which reduces the number of organoamine grafted in ethanol.

In order to further prove the effects of the solvents in grafting ofdifferent concentrations of organoamine groups and the cooperativeeffects by the organoamine and residual silanol groups to catalyze theHenry reaction, additional experiments involving grafting of additionalorganosilanes in ethanol and toluene onto AP-E1 were carried out asshown in FIG. 38. The AP-E1 sample was chosen because it contained asignificant number of silanol groups and its catalytic efficiency wasthe highest. First, 3-aminopropyltrimethoxysilane (APTS) was graftedonto AP-E1 in ethanol and toluene to result in AP-EE1 and AP-ET1,respectively. This grafting procedure decreased the number of silanolgroups in the materials but increased the organoamine groups.

Secondly, a 3-cyanopropyltriethoxysilane in ethanol and toluene was alsografted onto AP-E1 to result in AP-EE2 and AP-ET2. This procedure couldonly decrease the residual silanol groups and it did not increase theorganoamine concentration in the samples. Furthermore, the 3-cyanopropylgroups do not significantly change the hydrophilicity of the materialsto catalyze the Henry reaction in nitromethane. These grafting ofadditional 3-aminopropyl and 3-cyanopropyl groups in the AP-E1 wasdetermined by TGA analysis. For instance, the TGA analysis indicatedweight losses in the range of 100-600° C. for sample AP-EE1 and AP-ET1to be 10.8 and 16.0%, respectively, whereas those for AP-EE2 and AP-ET2were, 10.1 and 10.6, respectively, as shown in FIG. 43B. Compared withweight loss for AP-E1 (10.7%), these results revealed that additionalgrafting organic groups on AP-E1 barely occurred in ethanol, while somegrafting did take place in toluene, as shown schematically in FIG. 46.Further analysis by XRD for these materials indicated that theirwell-ordered mesoporous structures remained intact.

Comparative investigations of the efficiency of these samples incatalysis revealed the importance of the silanol groups and ethanol as asolvent for grafting again. While AP-EE1 and AP-EE2 showed only littlereduction in their catalytic efficiency and surface areas, samplesAP-ET1 and AP-ET2 showed significant reduction in their catalyticefficiencies and surface areas, as shown in FIG. 46 and Table 12.Furthermore, sample AP-ET2, which contained 3-cyanopropyl groups at theexpense of silanols, showed even significantly lower efficiency comparedto AP-ET1, which contained a corresponding number of 3-aminopropyl atthe expense of the silanols.

The applicants believe that the reduction of the catalytic efficiency inAP-ET1 and AP-ET2 is due to significant decrease in their silanol groupscompared to the AP-EE1 and AP-EE2, and an indication of the importanceof silanol groups and high surface areas for enhanced catalyticefficiency. The slightly higher catalytic efficiency of AP-EE1 comparedto AP-EE2 was due to the additional organic groups in the former beingcatalytically active 3-organoamine sites, while the additional organicgroups in the latter being inactive 3-cyanopropyl groups. Consequently,there would be more chances of cooperative interaction by organoaminesand silanols in AP-EE1 than in AP-EE2 (also in AP-ET1 than AP-ET2).These results further corroborated the importance of less number oforganoamines, more silanols, higher surface areas and the involvement ofsilanols and organoamines in the materials to cooperatively catalyze theHenry reaction as a bifunctional catalyst.

In order to understand the cooperative effects by the bifunctionalgroups, it is also worth comparing the number of catalytic sites withother materials in the literature to the best of the applicants'knowledge, our catalysts AP-E1 and AAP-E1 have shown the highestefficiency for the Henry reaction compared to any mesoporous materialreported either by grafting or co-assembly methods. The most efficientcatalyst previously reported by Diamcheli et al. in Tetrahedron Lett.2001, 42, 2401-2403 involved grafting of excess organosilanes in tolueneonto calcined mesoporous silica, and it had about 1.36 mmol —NH₂/g,which is a comparable value to our most efficient catalyst, AP-E1.

The number of Si—OH groups in the Diamchelli catalyst was not reported.Since the grafting was done on a calcined MCM-41 and in toluene underreflux, we believe that the number of Si—OH must be presumably muchlower than our AP-E1 sample. On the other hand, organoaminefunctionalized samples synthesized by Lin et al. in J. Am. Chem. Soc.2004, 126, 1010-1011 via co-assembly method contained triamine groups.We believe that the co-assembly synthesis would result in large numberof silanol groups and consequently significant cooperative effect;however, these issues have been overlooked previously by Lin et al.Despite the possible presence of such cooperative effects in thematerials reported by them, their catalysts still have much lowerefficiency compared to the applicants' acid-base bifunctional catalysts.The applicants believe that this may be due to their relatively inferiormesostructures, as can be inferred from their XRD patterns as well aspossible weak cooperative interaction due to the longer separationdistance between the silanols and the primary amines of thesetriamine-functionalized materials.

In the Henry reaction catalyzed by these acid-base bifunctionalcatalysts, an appropriate solvent such as nitromethane and a highertemperature were also found to increase the catalytic efficiency, asindicated in Table 12. Additionally, FIG. 47 is a temperature dependentcatalysis time plot of the organodiamine-functionalized mesoporousmaterials AAP-E1 at 90° C., AAP-T1 at 90° C., AAP-E1 at 50° C., andAAP-T1 at 50° C. By way of example, it can be seen that the reactionperformed at 50° C. resulted in three times less yield in the samereaction time compared to the reaction performed at 90° C. To the bestof the applicants' knowledge, this is the first time detailedtemperature and time plot studies for Henry reaction catalyzed byorganoamine-functionalized mesoporous materials have been studied. Thisstudy allows the rational design and synthesis of optimized cooperativeand efficient recyclable catalysts. For instance, studies ofrecyclability of our acid-base bifunctional catalyst, AP-E1 haveindicated an efficiency of about 100, 98.2, 97.5, and 97.4% in 15 minreaction time.

In summary, the applicants have discovered certain effects ofsite-isolation, concentrations and separation distances of functionalgroups in bifunctional acid-base catalysts on the cooperative catalyticproperties and efficiencies of the materials in base-catalyzed Henryreaction. This was achieved by comparative studies of a series oforganoamine functionalized samples containing various concentrations oforganomonoamine (or organodiamine) and silanol groups synthesized bysimple grafting of organomonosilane onto mesoporous silica using ethanoland toluene as solvents. The organoamine-functionalized materialssynthesized in ethanol have resulted site-isolated organoamine groups orless number of organoamine groups and large numbers of residual silanolgroups (organoamine:silanol ratio of 1:4-5). The resulting 3-aminopropyland 3-aminoethyl(3-aminopropyl) functionalized samples cooperativelycatalyzed the Henry reaction between p-hydroxybenzaldehyde andnitromethane to completion within ˜15 and 20 min and with a TON value of37.5 and 7.6, respectively, in 15 min reaction time.

To the best of the applicants' knowledge, the catalytic efficiencies ofthese materials have been the highest ever to be reported with at least3-6 times more turnover numbers than the corresponding control samplessynthesized in toluene. Control catalytic experiments by MCM-41 sample,which contain no organoamines resulted in no Henry reaction. Furthergrafting of organosilanes onto the residual silanol groups of theethanol product resulted in little additional organic groups when thegrafting was done in ethanol again but a significant increase of organicgroups in toluene.

FIG. 48 is a schematic representation of the relative efficiencies incatalysis of the Henry reaction by the applicants' monoamine and diaminefunctionalized mesoporous catalyst samples grafted in ethanol andtoluene. From our studies, we have determined that a ratio ofsilanol:organoamine of 5:1 results in the highest acid-base cooperativeeffect and the highest catalytic efficiency in Henry reaction.Furthermore, this cooperative effect by the organoamine and the silanolgroups and the efficiency of the catalysts was found to increase whenthe distances between the two functional groups is shorter. Thecatalysts were also found to be highly recyclable with only a veryslight decrease in the efficiency of the materials after four cycles. Tothe best of our knowledge, this is the first time that ethanol has beenused for grafting organoamines (and organosilanes) on the surfaces ofmesoporous silica materials. Our detailed time plot studies for Henryreaction by mesoporous materials have also been disclosed herein .

This simple synthetic approach is expected to allow the synthesis ofother efficient bifunctional materials and nanoporous solid catalystsvia a low temperature (78° C.) facile synthesis in a moreenvironmentally friendly solvent, ethanol, as compared to thetraditionally and more commonly used toluene solvent at 110° C. Thissynthetic approach can be adapted to the synthesis of highly efficientcatalysts with optimized cooperative and synergistic properties and thatare suitable for a number of industrial applications.

It is, therefore, apparent that there has been provided, in accordancewith the present invention, multifunctional mesoporous catalystcompositions and methods of preparation therefor. While this inventionhas been described in conjunction with preferred embodiments thereof, itis evident that many alternatives, modifications, and variations will beapparent to those skilled in the art. Accordingly, it is intended toembrace all such alternatives, modifications and variations that fallwithin the spirit and broad scope of the appended claims.

1. A multifunctional catalyst comprising a mesoporous substrate havingspatially distributed cooperative acid groups and base groups grafted tothe substrate.
 2. The catalyst of claim 1, wherein the acid groups aresilanol groups.
 3. The catalyst of claim 1, wherein the base groups areorganoamine groups.
 4. The catalyst of claim 3, wherein the organoaminegroups are organomonoamine groups.
 5. The catalyst of claim 3, whereinthe organoamine groups are organodiamine groups.
 6. The catalyst ofclaim 3, wherein the organoamine groups are 3-aminopropyl groups.
 7. Thecatalyst of claim 3, wherein the acid groups are silanol groups.
 8. Thecatalyst of claim 3, wherein the organoamine groups are spatiallydistributed at a density of between about 6 percent to about 15 percentof available sites.
 9. The catalyst of claim 8, wherein the ratio ofsilanol groups to organoamine groups is between about 2:1 to about 6:1.10. The catalyst of claim 9, wherein the ratio of silanol groups toorganoamine groups is about 5:1.
 11. The catalyst of claim 1, whereinthe base groups are selected from 3-aminopropyl,2-aminoethyl(3-aminopropyl), and 3-cyanopropyl, and combinationsthereof.
 12. The catalyst of claim 1, wherein the catalyst isbifunctional and is comprised of silanol groups and organoamine groups.13. The catalyst of claim 1, wherein the catalyst is trifunctional andselective and is comprised of silanol groups, base groups of firstorganic groups and secondary organic groups.
 14. The catalyst of claim13, wherein the base groups of first organic groups are organoamines.15. The catalyst of claim 13, wherein the secondary organic groups arehydrophilic groups.
 16. The catalyst of claim 13, wherein the secondaryorganic groups are hydrophobic groups.
 17. The catalyst of claim 13,wherein the secondary organic groups are selected from ureidopropyl,3-mercaptopropyl, and methyl groups.
 18. The catalyst of claim 13,wherein the molar ratio of the secondary organic groups and the basegroups of first organic groups is between about 1:1 to about 9:1. 19.The catalyst of claim 1, wherein the substrate is mesoporous silica. 20.The catalyst of claim 19 wherein the mesoporous silica is selected fromthe group consisting of MCM-41 and SBA-15.
 21. A selective trifunctionalmesoporous catalyst comprising a substrate having spatially distributedacid groups, base groups of a first organosilane grafted to thesubstrate, and secondary organic groups of a second organosilane graftedto the substrate.
 22. A method of making a multifunctional catalystcomprising the step of postgrafting aminoorganosilanes in a spatiallydistributed manner onto a mesoporous substrate.
 23. A method ofperforming a nitroaldol reaction comprising the step of reacting analdehyde and nitromethane in the presence of a multifunctionalmesoporous catalyst comprising a substrate having spatially distributedcooperative acid groups and base groups grafted to the substrate.